Ronaldo, who spent six years in Manchester before his move to Madrid in 2009, admitted that the tie could go either way.
The 27-year-old also spoke of his love for United and his excitement at returning to Manchester.
"On the day of the draw I was out training and had this strong feeling that we were going to get Manchester United," Ronaldo told The Sun. "I was very happy. It's a tough match that could go either way.
"Manchester was my home and is still 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 happy to be going back to Manchester."
The first leg of the last 16 tie is in Madrid on February 13, before the return leg at Old Trafford three weeks later.