Ronaldo scored 117 goals for United between 2003 and '09 before leaving for Real Madrid, and he suggested that he had contemplated returning to Old Trafford.
"It was true that Rio spoke to me a lot," the 28-year-old told reporters following the FIFA Gala in Zurich, in comments published by several British national newspapers on Tuesday. "Rio is a great friend of mine.
"We played many years together at Manchester United and we were neighbours when I was there in Manchester. He's a fantastic guy and tried to change my mind.
"I did think about United. They are still in my heart. It's a club where I played for six years and I love that club. I have a lot of friends there and I wish them the best."
Ronaldo scored in each leg as Real knocked United out of last season's UEFA Champions League in the Round of 16, but he pointedly declined to celebrate on each occasion.
Rio in awe of Ronaldo and Messi
Ferdinand corroborated Ronaldo's story, writing on his Facebook page that he "tried and failed to twist his ear".
The former England defender added: "Cristiano is living proof that no matter how much talent you have as a youngster, you have to work hard in order to be successful. I'm still truly astonished by the drive and determination to stay at the top, by not only Ronaldo but [Lionel] Messi too. It's been a joy to witness these two push each other week in, week out."
In a nod to a chant still aired by United fans at Old Trafford, Ferdinand concluded: "Viva Ronaldo. P.S - I tried and failed to twist his ear."