Ronaldo mocked Xavi this week over his lack of individual honours.
Eto'o, who played with Xavi at Barca, told Cadena SER: "If the Ballon d'Or was fair, Xavi would have won five or six.
"He deserves all the respect in the world."
Barca face another of Eto'o's former clubs, Leganes, this weekend.
He added: "If 'God' Messi wants to play, we will find it very difficult to win on Saturday."