Ronaldo, who was instrumental as Brazil won World Cup 2002, thinks that the youngster will return home next summer better than ever.
"He has evolved and I am sure he will evolve even more," Ronaldo told reporters.
"If he keeps getting better he will be the best player in the world.
"I'm sure he'll be coming to Brazil [for the World Cup] an even better player."
Ronaldo added that Neymar's teammate Lionel Messi is the current best player in the world.