He began his professional career withAthletic Bilbao, debuting aged 16 in 2009 as their youngest player in a competitive match. Due to his style of play and stature, as a teenager he was dubbed "the SpanishMessi" by the media.[2] He helped the team reach the final of theUEFA Europa League in2012 and played inCopa del Rey finals in2012,2020 and2021, but finished on the losing side each time. In 2022 he became the sixth player to make 500 appearances for the club, and lifted the Spanish Cup as captain in2024, a few months before leaving to end a 19-year association. Following his departure, he joinedSan Lorenzo of Argentina.
Muniain made his first-team debut on 30 July 2009, in aUEFA Europa Leaguequalifying match againstBSC Young Boys: he entered the field as a 59th-minutesubstitute forGaizka Toquero in an eventual 1–0 home defeat, thus becoming the youngest player in 94 years to wear Athletic's shirt in an official game at 16 years, 7 months and 11 days old,[7] only behindDomingo Acedo who scored on his debut in 1914.[8] One week later, in the return leg inSwitzerland, he netted his first goal, in a 2–1 win that qualified for the playoff rounds; he again entered the club's record books as the joint-second-youngest player to find the net (16 years, 7 months and 18 days) in a competitive match – behind Acedo and level withAgustín Gaínza[9]– and the youngest everin a European match.[10][11]
Another record fell on 30 August 2009, as Muniain started in the 1–0 home victory overRCD Espanyol,2009–10's opener, becoming the youngest player to have donned the club's shirt inLa Liga (overtakingPatxi Ferreira).[12] Two weeks later he scored again in European competition, 3–0 at home againstFK Austria Wien, after a good team move involvingAndoni Iraola and veteranJoseba Etxeberria.[13]
On 4 October 2009, Muniain became the youngest player to score in a first division match as he achieved that feat in a 2–2 draw atReal Valladolid, aged 16 years and 289 days[14][15]– that record was surpassed byMálaga CF'sFabrice Olinga in August 2012.[16] On 1 December he signed his first professional contract, running until June 2015.[17] On the 6th, after nearly one month out due to injury, he returned to action, scoring as a 51st-minute substitute to give his team the lead, albeit in a 2–1 loss toValencia CF. Heset up both goals in the next game, a 2–1 win atReal Zaragoza,[18] and finished hisfirst senior season with 35 appearances and six goals across all competitions.
Muniain was an undisputed starter in the2010–11 campaign, featuring as a left winger for theJoaquín Caparrós-led side. On 17 April 2011, he scored alast-minute goal in a 2–1 away defeat ofCA Osasuna in his hometown;[19] he was initially booked for taking his hand to his ear during his celebrations (before signing for Athletic he played forUDC Txantrea in Pamplona, and always considered Osasuna a rival organisation. He did clarify that, just because he had affection for a particular organisation, it did not mean he held any animosity towards any others)[20][21] which meant a suspension for his fifthyellow card of the season,[22] but it was later lifted. Now allowed to take part in the following matchday, thederby againstReal Sociedad, he netted another in a 2–1 home victory.[23]
Muniain took part in 58 games overall in2011–12, scoring on nine occasions as theLions reached both theEuropa League and theCopa del Rey finals.[24] In early 2012, he was linked with a move away from Athletic, although a move never materialised as he did not push for a move with three years still left on his contract.[25] He scored just once in 33 league appearances thefollowing campaign, netting the only goal on 10 March 2013 in a home win over Valencia which eased doubts over a possible relegation battle.[26]
On 1 December 2013, Muniain was again the sole name on the scoresheet at the newSan Mamés Stadium, to handFC Barcelona their first league loss ofthat season.[27] Eighteen days later, he celebrated his 21st birthday by grabbing a brace in a 4–0domestic cup home victory againstRC Celta de Vigo, which signified his team progressed through to theround of 16 4–1 on aggregate.[28] In that period, media reports suggested that his progression as a footballer in his 20s had slowed after showing such high potential as a young teenager.[29][30]
On 4 April 2015, during a game againstSevilla FC, Muniain suffered the first serious injury of his career, being sidelined for several months with ananterior cruciate ligament ailment to his left knee[31]– this meant he was unable to take any part in the year'sSpanish Cup orSupercopa de España finals.[32] After suffering some setbacks in his recovery process[33][34] he returned to action on 20 December, replacingIñaki Williams for the last minutes of a 2–0 home defeat ofLevante UD.[35]
Muniain successfully regained his first-team place in December 2015 and made 86 further appearances between then and 28 September 2017, when he suffered another serious ACL injury (this time to his right knee) in the closing stages of aEuropa League fixture at home toFC Zorya Luhansk, potentially ending his season.[36] After an absence of just over six months, he returned to action as a substitute in adomestic league match againstVillarreal CF on 9 April 2018, scoring his side's third in a 3–1 away win.[37]
Muniain signed a new deal with Athletic Bilbao in November 2018 to run until summer 2024, as his link was set to expire;[38] unusually, it did not include anybuyout clause.[39] He said: "I didn't want a release clause because I do not want to have a price or be for sale. I want to go hand in hand with Athletic to the end... I want to be here for the rest of my career helping the club achieve nice things."[40] Following the departures ofAnder Iturraspe andMarkel Susaeta in summer 2019 he was appointed as the clubcaptain,[41] and also reached the milestone of ten years with the first team.[42]
In early 2021, with the team playing a more attacking style under new coachMarcelino García Toral, Muniain recorded eight assists in three competitions between 17 January and 15 February (bettering his total for some entire seasons previously),[46] including two in theSpanish Supercup final as his team won the trophy.[47] During April of that year he took the field in the2020 (delayed due to theCOVID-19 pandemic) and2021 Spanish Cup finals, both played in an emptyEstadio de la Cartuja – the same venue as the Supercup win – due to the pandemic restrictions. Athletic lost the first match 1–0 to Real Sociedad,[48] with Muniain breaking a footballing superstition before kick-off by touching the trophy (considered to be 'bad luck')[49] but praised for his sportsmanship for staying on the pitch after the final whistle to applaud the winners.[50] A pre-match injury doubt for the second final two weeks later, he stated to the press "Cups and trophies are not won or lost because one touches it or not. They are won on the pitch, and that is the only reality", but this time it was noted he kept his hands well away from the prize;[51] nevertheless his team were defeated 4–0 by Barcelona and he was withdrawn at half-time with the score at 0–0[52] and did not feature again that season, missing the last eight league fixtures.
On 31 October 2021, Muniain scored a late equaliser in the Basque derby via afree kick and was again conspicuous for his sportsmanship in consoling the opposing goalkeeperÁlex Remiro, a former Athletic player whose error had contributed to the goal.[53] In February 2022, it was assessed that he had created 60 scoring chances inthat league campaign and 72 in all competitions, the most by any player by both counts.[54] Despite knocking both Barcelona and Real Madrid out of the domestic cup, they lost inthe semi-finals to Valencia, and finished the league campaign in eighth, just out of the European qualification places.[55]
Muniain made his 500th appearance for Athletic on the first matchday of2022–23 againstRCD Mallorca, reaching the milestone at a younger age than the five other players to do so.[56][57] He was honoured in a reception after that match,[58] and was presented with a memento by two of those men –José Ángel Iribar and Susaeta – on the pitch before the next fixture against Valencia six days later.[59][60] After a promising start under returning coachErnesto Valverde the team again finished eighth and lost narrowly in thecup semi-finals (this time to Osasuna);[61] he featured regularly but became less of a habitual starter, coming off the bench in 11 of his 30 league appearances.[62]
Athletic also began2023–24 strongly, but Muniain was selected rarely during the first half of the season, with Valverde opting forOihan Sancet as the starting attacking midfielder and eitherÁlex Berenguer or rookieUnai Gómez as an offensive substitute.[63] On 30 September against Real Sociedad, he reached 542 appearances for the club, surpassingTxetxu Rojo's record for an outfield player (albeit with far fewer minutes overall)[64][65] and trailing Iribar alone.[66] In theSpanish Cup final against Mallorca, he was brought on as a substitute at the start of extra time with the score at 1–1. He narrowly missed the target with a free kick, and then scored his penalty in the subsequent shootout; Berenguer converted the winning kick, and the team claimed the trophy for the first time in 40 years.[67]
Although there was some expectation that he may remain for the upcoming European campaign,[68] on 24 April 2024 Muniain announced he would leave Athletic on 30 June, marking the end of his 15-year tenure in which he became the second-highest appearance maker in the club's history (560 matches); he declared himself happy with the timing of his departure having won the cup,[69][70] and it was speculated that he would move abroad to continue his playing career.[68] His appearance record stood for just over a year before being overtaken in February 2025 by long-time teammateÓscar de Marcos, who had also replaced him as captain.[71]
Muniain made several trips to Argentina, declaring that he wanted to play in that country, and held talks withLeandro Romagnoli, the coach ofSan Lorenzo de Almagro; on 3 September 2024 he signed a contract running to December 2025, with the latter declaring that the former's role would be as a playmaker located behind the striker.[72] He became the tenth Spaniard to play for the club, one of the most prominent beingÁngel Zubieta who also represented Athletic Bilbao.[73]
Muniain earned 31caps for the under-21s, which was a national record[79] for three years before being surpassed byGerard Deulofeu.[80] In 2019, after showing fine form for his club, he was selected in the senior squad for twoUEFA Euro 2020 qualifying matches;[81] he played his second match more than seven years after the first, as well as his competitive debut, as a substitute in a 2–0 victory overMalta on 26 March.[82]
Muniain has two older cousins who are also footballers, were both Athletic youth players and were briefly his teammates at Bilbao Athletic.[84][85]Adrien Goñi, amidfielder, made a handful of first-team appearances before embarking on a career in the Spanish third division.[86][87][88]Winger Julen Goñi eventually moved toBarakaldo CF also in that tier.[89][90][86]
Having vowed to have the Europa League trophytattooed on his body if Athletic Bilbao won the 2012 final,[24] which did not happen, Muniain did have theSupercopa de España trophy 'inked' on his leg in 2015 following the team's victory (albeit he took no part in the matches due to injury).[92] Another tattoo on the rear of his neck,XIX,[93] (19 inRoman numerals) refers to his birth date and that of his brother,[94] and was his original Athleticsquad number for several seasons although he wore 27 as a promoted youth player in his breakthrough campaign,[3] and in 2016 changed to the traditionalplaymaker's number 10[95] which he held until leaving the club eight years later.[96]
^Acedo, Diego (19 December 2013)."Muniain aúpa al Athletic a octavos" [Muniain propels Athletic to last-16].Marca (in Spanish). Retrieved20 December 2013.
^Herrán, Alfonso (30 July 2019)."Muniain: 10 años del 10 del Athletic" [Muniain: 10 years of Athletic's 10].Diario AS (in Spanish). Retrieved27 September 2019.
^abRodríguez Beltrán, Javier (24 April 2024)."Muniain jugará en el extranjero" [Muniain will play abroad].Diario AS (in Spanish). Retrieved24 April 2024.
^Ortiz de Lazcano, Javier (30 April 2011).""Todavía soy un crío"" ["I'm still a baby"].El Correo (in Spanish). Retrieved25 May 2021.
^abcZárate, Óscar (31 March 2012)."Iker Muniain: 'El Messi del Botxo'" [Iker Muniain: 'The Messi from Botxo'].Mundo Deportivo (in Spanish). Retrieved7 March 2017.