Atletico Madrid boss Quique Sanchez Flores said after his side's 3-0 defeat to Barcelona that Messi was "the Di Stefano of the 21st century". Argentina-born Di Stefano was Madrid's leading star as they won the first five European Cups.
However, Valdano - who won the World Cup with Argentina in 1986 - believes Ronaldo is the player to continue Di Stefano's legacy.
"It is not Messi," he said. "It is Cristiano Ronaldo, who significantly wears the same shirt as Di Stefano. He is a very important player who is set to make history at this club.
"We wouldn't swap Cristiano for anyone, although one must recognise that both he and Messi are two very high-quality players and it is a privilege to have them in La Liga."
Ronaldo scored twice in a 4-1 victory over Real Sociedad on Sunday and Jose Mourinho had words of praise for the player.
"Ronaldo's run in La Liga will be fantastic even if he doesn't score another goal in the remainder of the season," he said. "I'd like to underline that. I say this to my men also. He always plays to the limit of his capabilities and ambitions. He gives his all for this team. It doesn't matter if he doesn't score. I don't have preference for him."