The Portugal captain was a cult hero at Old Trafford before departing the Premier League club to join Real in 2009 for a world-record fee at the time.
Ronaldo has taken his game to another level since joining the European champions and has no intention of leaving Santiago Bernabeu for the time being.
The 29-year-old, though, would welcome the opportunity to return to United before he hangs up his boots.
"I love Manchester," he told the Daily Telegraph. "Everyone knows that. Manchester is in my heart.
"I left many good friends there. The supporters are amazing and I wish I can come back one day."
Ronaldo picked up the FIFA Ballon d'Or in January and went on to break the record tally for goals in a UEFA Champions League season, finding the back of the net 17 times as Carlo Ancelotti's won the famous trophy for a 10th time.
And the former Sporting Lisbon man is as hungry as ever to break more records this season.
He said: "Well, it was a fantastic year. We won the Champions League, we won La Decima, the trophy that Real Madrid had been looking for a lot.
"So this season we're going to try to do the same, to win the Champions [League] again, to win La Liga. And in terms of individual achievements I'm going to try to break my own records. I know it's tough, but I'm going to try."
