Nearly four years after leaving for Real Madrid in a world record £80million deal, Ronaldo will be back at United on March 5th to try and help his current team knock his old one out of the UEFA Champions League.
It is bound to rekindle memories of the brilliance Ronaldo brought to the Premier League in his six-year stint with the Red Devils, as well as trigger thoughts about whether it ever could be revived.
Ferguson has spoken optimistically about the prospect in the past - and he still won't rule it out completely.
However, in sober analysis, the Scot is not convinced it will ever happen.
"I don't see it," said Ferguson. "I would love to think it. Maybe when he is about 39 and you are coming past my grave, but it is fanciful thinking really.
"First of all how much would it take to get him from Real Madrid?
"Secondly I don't think there is any chance they would want to sell him anyway.
"You never know. I don't know when his contract finishes and he may want to go to another club at some point in his career. Of course I would hope he'd want to come here. But that is a long way off."
Ronaldo's return is fixed though. And Ferguson knows the player he spent £12.24million on to sign from Sporting Lisbon as a 17-year-old in 2003 represents a significant threat to his side's hopes of progression in Europe's most prestigious competition.
So much so that Ferguson's first thought when he heard the draw was to check the small print of that world record transfer.
"Our contract with Real is that he can't play against us," laughed the Scot. "I think it would be a disgrace if he played against us. It would be no loyalty."
Ronaldo is assured of a rapturous reception from the Old Trafford faithful, as warm as the one he gave Ferguson when they met at the Lowry Hotel in Manchester recently.
The wide-man has already confirmed an intention not to celebrate any goals he scores in the two-legged tie, although Ferguson would not be too bothered if the Red Devils supporters attempt to put Ronaldo off when the action starts.
"He will get a great reception when he comes onto the pitch at Old Trafford, quite rightly, after that they can boo him as much as they like," said Ferguson.
"We are proud of the part we played in his career.
"We did very well to get six years out of a boy when he came to us at the age of 17."