To say that Guiu hit the ground running after breaking into the Barcelona first team would be a major understatement.
The La Masia graduate made an instant impact after coming on in the 79th minute of Barcelona's La Liga match against Athletic Bilbao in October 2023, scoring just 33 seconds later to earn Xavi's team a 1-0 victory.
His path to the senior side was much less straightforward, however. Impacted by multiple growth spurts during his teenage years, the diminutive frontman was not always a regular starter at youth level.
"He missed a lot of games," Albert Capellas, Barcelona's former assistant director of youth football, told Sky Sports earlier this year. "He could not train.
"What happens at a lot of clubs, if you cannot train or play, maybe you have to leave. \[But\] at Barcelona, we know the level of the players, we give them time."
The Catalan club's patience played into Guiu's hands. He made a further six appearances for the senior team in 2023-24, scoring again in a 3-2 defeat by Royal Antwerp in the Champions League.
"Marc Guiu is a finisher," added Capellas. "\[He\] is not a player who has unbelievable skills one against one, who can dribble past players. He is another type of player, but he is exceptional in his position. He has the nose to score goals."
In June this year, Chelsea reached an agreement to activate his £5m release clause before signing the youngster on a five-year contract, with an option of a further year at Stamford Bridge.