Spanish media "Maca" reported that Mastantono will arrive in Madrid this weekend to start his career as a Real Madrid player. His underage status prevents him from joining training when Real Madrid resumes training next Monday. Therefore, it was not until August 14 that he would become 18 years old that he could integrate into the team and start his Real Madrid career.

It is reported that Mastantono may take over Mbappe's No. 9 jersey. Bellingham's injury provided Mastantono with the opportunity to perform from the initial stage and strive to win the trust of Harvey Alonso.

Mastantono will become the 14th player to play for Real Madrid and River Plate. He is also the fifth player to play for Real Madrid from River Plate youth training, and the fourth player to transfer directly from River Plate to Real Madrid.

Mastantono joined the Riverbed in 2019 at the age of 12, after he was excavated during a trial in Asul in 2017. In 2023, he signed his first professional contract with a penalty of 30 million euros. A month later, he was recruited by the coach of the River Plate to practice with the first team.

Mastantono made his debut in the League Cup against the Argentine Youth Team on January 28, 2024, and became the youngest player in River Plate history to score in official matches at the age of 16 years, 5 months and 24 days in February.