Real Madrid announced on Wednesday that Cristiano Cruz had joined the club for an undisclosed fee.
It is the latest of several transfers to be completed in recent weeks for the Portuguese international, who is currently on loan at Real Madrid.
Ronaldo’s current contract expires in 2020.
He scored 20 goals in 35 games this season, helping Real Madrid to second place in La Liga.
His move was confirmed by the club on Wednesday morning.
Cristiano Cristiano (Real Madrid) – La Liga 2016/17 season: 20 goals, 9 assists, 1 goal in 20 league appearances, 6 goals in the Copa del Rey semi-finals, 2 goals in 5 Champions League matches, 1 assist in 7 Champions League group games, 2 assists in 3 Copa Del Rey quarter-finals Cristiano is currently with Real Madrid, having joined the Spanish club as a 17-year-old.
Ronaldo has already been linked with moves to Chelsea, Manchester City and Liverpool, with the former Manchester United star set to make his first-team debut against Arsenal on Sunday.
He also spent time on loan with Real Zaragoza in Spain, where he scored three goals in 20 games.