By Andy May
The Portuguese attacker was linked strongly with a move back to Old Trafford during the most recent European transfer window - reports that Ferguson has confirmed were not false.
"Although I was not involved directly, I thought that there may have been a chance in the summer [for Ronaldo to sign for United] but it seemed to pass away quite quickly.
"I do not think he will return now he has signed a new [Real Madrid] contract."
Ferguson, now a United Director who freely admits to helping manager David Moyes when required, gave Ronaldo his big break in England in 2003. Then a teenager, the Portuguese was signed after impressing Ferguson and United's players and coaching staff in a pre-season friendly involving his old team Sporting Lisbon.
"Cristiano came as a boy aged seventeen and he was a remarkable human being - in terms of his ambition to keep improving.
"Almost every week you would see a new quality added and he became a great player to train with."
In Ferguson's newly released book - a second autobiography reflecting on his last fourteen years as United manager - the 71-year-old describes Ronaldo as the most 'gifted' individual he worked with during his entire Old Trafford career.
"Cristiano was the most gifted player I managed. He surpassed all the other great ones I coached at United - and I had many.
“The only ones who could be placed near him would be a couple of the home-produced players, Paul Scholes and Ryan Giggs, because they contributed so prodigiously to Manchester United for two decades."
Real Madrid paid £80million to sign Ronaldo from United in 2009 and the Portugal captain agreed a new contract at the Santiago Bernabeu in September in a deal that expires in 2018 when the player will be 33 years old.
See the first part of our exclusive Sir Alex Ferguson interview on Fox Sports Central on Wednesday evening - check television listings for timings in your country.