The Portuguese icon went onto score 118 goals in 292 games across all competitions, helping the Red Devils to a series of major trophies, including the Premier League and the Champions League.
Ronaldo is no doubt a club legend, even if he joined Real Madrid in the summer of 2009. The winger bagged 27 goals in his second spell at the club before leaving for Saudi Arabia, where he now plays for Al-Nassr.
A return is unlikely for the 40-year-old but McCarthy spoke to BestBettingSites.co.uk and said he believes that the legendary forward should come back to wave one final goodbye to fans who cherish him so much.
"Oh, definitely. You know what he's achieved since he came to the club, and where his career then kind of exploded even more when he went to Real Madrid. So he has only good memories at Man United.
"I think the manner that he left, it wasn't a fitting manner for such an unbelievable, world-class player of his stature. So if that is the case that United get to play against Al Nassr, it will be a nice way for him as well to reconnect with the club that he's achieved so much with, and the club that put him on the map in world football.
"So it would be a nice way for him to say goodbye to his teammates. Because I know for a fact after that interview dropped he just left and we never saw him again. He never got to say goodbye to the players, to his teammates and to the technical staff that was there.
“But this might give him a proper opportunity to reunite with the United faithful again. And the fans that will be there will give him a nice farewell, because that's what he deserves for what he's achieved at the club."
Ronaldo spent six glorious years at United and as he eyes retirement in a few years time, he may want to make the move back to the Premier League side who may love to have him on the side providing he takes a large pay cut.