Real Madrid legend Jorge Valdano believes Cristiano Ronaldo's unrivalled ego is the main motivation behind his incredible list of achievements.

Ronaldo declared himself the "best player in history" after winning a fifth Ballon d'Or last week, equalling Lionel Messi's record mark.

His comments sparked fresh discussion from current and former players as to his place among the game's greats and how he compares to the Barcelona star.

Valdano, who enjoyed successful stints with Los Blancos as both player and manager, believes Ronaldo is fuelled by his inner-drive rather than his rivalry with Messi.

"Cristiano has the most profitable ego in the history of football," Valdano told Spanish broadcaster Onda Cero.

"He has an extraordinary amount of confidence in himself and that's allowed him to improve a lot.

"There are people who are confused by their ego and it turns into an excess of confidence. He puts it to work every week.

"Messi and Cristiano have opposite profiles but I do not think either of them accepts advice. They are capable of doing things few have done in the history of football."