Ronaldo, though, claims that the youngster will be playing for the Catalan club in the near future.
"He has the potential [to become one of the world's best players]," Ronaldo told Tuttosport.
"But we have to assess his impact on European football when he arrives at Barcelona.
"The first year will be difficult for him, but I'm confident that when he adapts he'll be one of the very best."
Ronaldo played for Barcelona for one season in 1996-97, scoring 47 goals in 49 games.