[3] He went on to join Barcelona themselves in the 2013–14 season, and progressed through the La Masia academy, and was called up to the senior squad for the first time in June 2023, ahead of pre-season matches against Celta de Vigo and Japanese opposition Vissel Kobe.
[4] Guiu made his unofficial debut for Barcelona in the latter game, coming on as a half-time substitute for Robert Lewandowski.
[16][17] On 1 July 2024, Guiu joined Premier League side Chelsea for a reported €6 million fee,[18] signing a five-year contract with the club.
In May 2023, he was called up by Spain U17 to compete in the 2023 UEFA European Under-17 Championship,[22] in which he became the competitions joint top scorer with four goals, alongside Paris Brunner, Robert Ramsak and teammate Lamine Yamal.
[25][26] Barcelona youth coach Iván Carrasco describes Guiu as a "classic '9', a specialist in the area who exploits his physical power".