Speaking ahead of his official presentation as a Real Madrid player on Monday following his world-record £80million move from United, Ronaldo was keen to hail the impact Ferguson has had on his career.
"He's been my father in sport, one of the most important factors and most influential in my career," Ronaldo said in an interview with Spanish newspaper Marca on Saturday.
Ferguson splashed out £12.24million to bring the teenage Ronaldo to United from Sporting Lisbon in 2003 and in six years under the Scot's tutelage, the Portugal international has developed into one of the best players on the planet.
Ronaldo severed his ties with United this summer to complete his move to Madrid, but the 24-year-old admits he will never forget what Ferguson did for him.
He added: "I have to thank him for all that he taught me. He's been fundamental. I'll always have great affection for him and he will occupy a special place in my heart.
"I'll also keep a very special memory of (United chief executive) David Gill and all the directors at United."
Ronaldo, who revealed he would be travelling to Manchester in the coming days to say his farewells to Ferguson in person, also had a message of thanks for his former fans at United.
"It was my home. I played there six seasons and I was always well liked by the United fans," he added.
"We won many things together. They always sang my song in the stands and I have to thank them for the affection they showed me during all the time that I played at Old Trafford. The fans of Manchester (United) are special."