He faced accusations he was axed by Sunderland owner Ellis Short for being a football 'dinosaur'.
O'Neill, 61, said: "You talk about dinosaurs - the biggest dinosaur in the game happens to be the best manager in the game. I'm talking about Alex Ferguson. Absolutely - there's no bigger dinosaur. He is 71 years of age, too.
"Also, it's interesting England turned to Roy Hodgson to become their new manager with all that vast experience.
"And QPR have turned to Harry Redknapp, so everybody has a shelf life but it doesn't depend on age."