The 28-year-old has two years to run on his deal at Madrid, who paid a world record £80million fee to prise him away from United in 2009.
Ronaldo hinted he might yet like to return to Old Trafford before his career ends, but denied suggestions a switch could come any time soon.
"Yes I really miss English football," he said during a promotional event in Singapore.
"For me it was one of the best years in my career when I was there at Manchester United. Everyone knows that.
"It is the club that is still in my heart. I really miss (the club).
"But now my life is in Spain. I'm enjoying playing there too. Part of my life is there. The future we never know.
"I'm really, really happy in the Spanish league at the moment."