The Portugal international enjoyed a hugely successful time at the Old Trafford side between 2003 and 2009 before leaving United for Madrid in a deal worth €94 million.
Nevertheless, the 29-year-old has nothing but fond memories of his time at the Premier League giants and is eager to return to the club where he made his name once his time at the Santiago Bernabeu ends.
"I love Manchester United. Everyone knows that - I have said it many times. Manchester United are in my heart. I left many good friends there, the supporters are amazing and I wish I can come back one day," Ronaldo told Daily Mail.
"I am happy here at Real Madrid and have four more years, but in the future you never know because they treated me unbelievably at United.
"I really did love being at Manchester United."
The prolific attacker then went on to discuss Louis van Gaal's side's difficult start to the 2014-15 campaign and stressed that he's confident they will improve following the arrival of Angel Di Maria and Radamel Falcao.
"Believe me, they will be a good team again, I’m sure of it. They are a great club. This sort of blip can happen. Bad moments and good moments. Manchester are passing through a bad moment.
"Last year it was a horrible season and this year they haven’t started well, either. But I do think they did well to buy Di Maria and Falcao.
"I think the team will be much better. I want to see them better because it is such a fantastic club and they deserve to be better.
"Manchester United have not started well, two points in three games, so they need quality players and Falcao is a quality player. And Di Maria, too."
United currently sit 14th in the Premier League table with two points from three games.