However, Mendes has insisted that the Portuguese's talent would stand alone in any era.
"The only things he lives for are his son, his family and football, in order to be the best in the world. That's his constant objective. No-one is more professional than he is. Players might match his dedication, but no-one can surpass him," he told ABC.
"He trains every day in order to be the best player in the world, and that's why he has won two Ballon's d'Or.
"He was a great player at both clubs (Manchester United and Real Madrid). The key has been the progress he's made at every stage of his career. For me, he'll go down in history as the best footballer of all time. In fact, for me he is already the best player of all time."
Ronaldo has scored 233 goals in 229 games for Los Blancos since joining in 2009.