Mastantuono, 19, played 35 games for Real Madrid after joining the club in 2025 from River Plate. He scored three goals for the Spanish side. The Argentine midfielder has quickly established himself at Fiorentina, scoring a hat-trick in a 4-2 win over Venezia in the Italian league. This achievement has made him the youngest Argentine to score a hat-trick in one of Europe's top five leagues, surpassing Lionel Messi's record.
Mastantuono's loan deal with Fiorentina does not include an option for the Italian club to buy him. Real Madrid sent the player on loan to give him more playing time and continue his adaptation to European football. The midfielder himself acknowledged that his first season at Real Madrid was complex, but he sees his move to Fiorentina as an opportunity to show his skills and help the Italian club.