The 29-year-old, who spent six seasons at Old Trafford, admits he would be open to returning to his former club and has praised the arrival of Louis van Gaal.
The 29-year-old joined Real Madrid from the Red Devils in 2009 after spending six seasons at Old Trafford.
"It was like my second family there, so I’ll not forget that the people treat me good," he said. "I love Manchester United and to go back ... with football you never know.
Ronaldo, who will not face United in Saturday’s preseason friendly in Michigan due to fitness concerns, admits he sees his former club as one of his favorites alongside Real Madrid.
"Manchester United are one of my favorite clubs, everyone knows that every time when I speak about Real Madrid I speak about Manchester United, I loved it there," Ronaldo told reporters.
"I was 18 years old when I joined, I won everything there, the people treat me like a god there so I appreciate that and, in the future, who knows."
However, Ronaldo reiterates that he is happy to remain at the Santiago Bernabeu for now.
"Of course, I’m happy at Real Madrid - it’s my home, my club - but Manchester United treated me unbelievable so you never know," he said.
Ronaldo believes United will prosper under Louis van Gaal’s guidance following their worst-ever Premier League campaign last season under fired coach David Moyes, who had replaced Sir Alex Ferguson in 2013.
"It will be a better season for sure. My feeling is Van Gaal is a fantastic coach, he showed that all the time for Netherlands, the team played unbelievable at the World Cup, and I hope that Man United come back like the people know," he added.