The new Queens Park Rangers defender has revealed in his new autobiography, #2Sides, that the fear of being on the receiving end of the famed Fergie hairdryer treatment made him a much better player.
Ferdinand recalls a Champions League game in 2006; United were away at Benfica and Cristiano Ronaldo was trying much to hard with little coming off. United lost the game and afterwards the 35-year-old revealed that the world class winger received a hairdryer that shocked even him.
He says: ‘‘I remember Ronaldo getting emotional one game when we played Benfica in Lisbon. He thought he had to prove to people in Portugal why he moved to United.
"The game became the Ronaldo show, he was trying to show his skills and nothing was coming off. We lost and afterwards the manager absolutely destroyed him. “Who the hell do you think you are”.
"I never saw England managers hammering David Beckham like that, or Stevie Gerrard or Frank Lampard or Wayne Rooney.
"It made me think, I could be next. I better stay on my toes. We took Fergie for granted, but now I see he was a genius."
Rio led a distinguished career with United after joining from Leeds United for £30 million in 2002, which was then a British record.
The West Ham academy graduate made 312 league appearances during his 12-year stint at Old Trafford, winning six titles, four FA Cups, two League Cups and one Champions League.
The only high profile run-in that the former England international had with the legendary manager was his decision not to wear an anti-racism shirt from the Kick It Out campaign. It was three months after the John Terry vs Anton Ferdinand court battle over a charge of racial abuse.
Ferdinand refused to wear the shirt on the grounds that they failed to support his brother in court; Ferguson reportedly broke into a foul-mouthed rant at the player before fining him a weeks wage.
However surprisingly for Sir Alex he later apologised and admitted his criticism was a mistake.