Ronaldo will face his old club in the Champions League.
He told The Sun: "Manchester was my home and still is in my heart. I love it. Because when people treat you very well you never forget that. And I will never forget United, the people who work there and the supporters.
"So I am so happy to be going back to Manchester.
"I will go and see my old house, see my Manchester friends - they're a kind of a family to me there and it will be great. It will be fun.
"And finally I will go to the club where I played for many, many years.
"It will be so nice. I still speak with quite a few of the United lads: Rio, Patrice, Nani, Anderson.
"The guys have all been joking with me. It will be great to see them again even though it is going to be a very difficult game.
"Manchester United are the best team in England, they are great. Every year they win something.