The retired striker has no doubt about his countryman's potential but insisted that he must play in Europe if he hopes to become the best player in the world
The 20-year-old sensation committed his future to Santos earlier in the year by signing a new deal that will expire in 2014, despite reported interest from Barcelona and Real Madrid.
Santos coach Muricy Ramalho recently rejected the notion that Neymar needs to play in Europe to fully realise his potential, but Ronaldo, who spent most of his playing career in the Old Continent, thinks otherwise.
"[Lionel] Messi is at a higher level than any other player on the planet," Ronaldo told TV Cultura.
"Neymar is our biggest talent. I believe that he can be better than Messi. There is still big room for improvement for him, but not if he keeps playing in Brazil.
"If he does not play abroad, it is clear that he will not be the best in the world. Although Brazilian football is growing, it still does not have the potential to impress abroad."
Neymar has eight goals in 16 appearances for Brazil.