The Real Madrid star experienced a good relationship with former boss Ferguson at Old Trafford before his move to Real Madrid in 2009, where the Portugal international made his name.
But - Fergie aside - Ronaldo claims that, though he is on speaking terms with Manuel Pellegrini and Carlo Ancelotti, he has not stayed close with many of his past coaches.
“The only friendship that I have with my former coaches is with Ferguson, with no one more,” Ronaldo told Portuguese TV channel TVI.
“I had a good relationship with Pellegrini, and Ancelotti also, with whom I get along very well.
“I’m not in football to have friends. I am here to succeed.”
The 29-year-old also commented on ex-Madrid coach Jose Mourinho – who is currently in charge of Chelsea – acknowledging that there was a "bad atmosphere" and that his tenure was "a difficult phase in personal terms and the club".
He added: "There were situations that were happening with other players, also with the fans.”
Ronaldo will miss the start of Portugal’s Euro 2016 qualification campaign due to concerns over the forward's fitness following a series of thigh and knee problems that the winger suffered at the end of last season.