Spanish club said in a statement, a 6 -year contract with the 17 -year -old player reportedly signed.
Right -wing player who started his football life in the River Plate infrastructure, recorded 11 goals in 62 games in the Argentina team.
Mastantiono is the youngest player to play in an official match in the history of Argentina.
According to the Spanish press, Real Madrid paid 45 million euros for this transfer for this transfer.