It seems incredible to think now but the Portuguese superstar was on the brink of a move to Pep Guardiola’s side before he sealed an emotional return home to Old Trafford.
And now, a report in the Daily Star has revealed the inside story of how United managed to gazump City to Ronaldo’s signature.
For six weeks, City had been in negotiations with Ronaldo's agent Jorge Mendes. They had failed in their pursuit of Harry Kane and they were ready to press ahead of the signing of Ronaldo from Juventus.
They had even agreed on a fee with Juve, believed to be £25 million, as well as personal terms. The paperwork had been drawn up.
Little did they know that United were planning their own move.
Executive vice-chairman Ed Woodward and commercial director Richard Arnold were given the green light from the club owners and went to work to finally re-sign Ronaldo at the fourth attempt.
One senior club official even said: "I couldn't accept him in sky blue. Ever. I'd rather cut my eyes out."
The ultimate Cristiano Ronaldo quiz
Therefore, the club threw everything they had at Ronaldo.
They must have known a return to the Theatre of Dreams would be difficult to turn down for CR7. However, they also must have known Ronaldo is motivated by success and trophies and would have more chance of both across the city.
His former teammates - including Patrice Evra and Rio Ferdinand - got in contact with him to persuade him not to join City but return to United.
Then, in the final week of the window, they played their trump card - Sir Alex Ferguson.
Fergie personally called Ronaldo - but it wasn’t for a lengthy chat about the situation.
Instead, according to the Daily Star, Ferguson simply said "don't join City" in a 20-second call before hanging up.
That was it.
But such is Ferguson’s pull that it worked a treat.
Ronaldo was “flattered” and instructed Mendes to complete the deal with United. Just days later, Ronaldo was home.
Guardiola was informed of the news minutes before a press conference he was giving ahead of Man City’s match against Arsenal.
He "struggled to contain his anger" after City's director of football, Txiki Begiristain, dropped the bombshell.
None of the journalists on the Zoom call knew it but Guardiola was bitterly disappointed and, in that very press conference, said: “In my personal view there are few players, Cristiano Ronaldo is included and (Lionel) Messi of course, who decide where they are going to play. They have the leading role in the negotiations in where they want to play.
"Cristiano will decide where he wants to play: not Manchester City, not myself. There are many things that right now look far, far away. I know today is a tough press conference for myself.
"These players decide. They knock on the door. They go. After that there are situations I cannot control, because it is not my business and I am focused to do what we have to do and the players we have right now."
Ronaldo had made up his mind with a little help from Ferguson.
Saturday’s Manchester derby could have been very different if the legendary Scot hadn’t said those three words.News Now - Sport News