The move for Mastantuono, which included a €43 million (£37m/$50m) fee, has been met with high expectations from Real Madrid fans. He remained at River Plate for the FIFA Club World Cup before his official switch to the Bernabeu after a transfer war between the Spanish club and PSG. Mastantuono's arrival comes at a time of key midfield injuries for Los Blancos, with Jude Bellingham and Eduardo Camavinga sidelined. This could open an immediate path for the young Argentine to be involved in the first team under manager Xabi Alonso.
Mastantuono became River Plate's youngest-ever goalscorer when he found the net in a Copa Argentina match in February 2024, at just 16 years old. He also scored a memorable free-kick against arch-rivals Boca Juniors.