The 17 year-old is a top target for Real Madrid this summer, though only after they refused to meet River's asking price a year ago.
AS says now Real are prepared to pay his €45m clause knowing PSG have made an attempt in recent days.
PSG coach Luis Enrique's call to the player set off all alarms in the Spanish capital. The idea was to wait until January, closely follow the progress of the teen, then decide whether it was worth it or not to pay such a high amount for a young player.
But no-one inside Real Madrid believed PSG and Lucho would make such an aggressive move this week.
As such, Real Madrid will now pay Mastantuono's clause and leave it with the player and River whether he moves to Spain this summer, or wait until January so the player can compete in the Copa Libertadores.