Ronaldo spent six years at Old Trafford under Ferguson, winning the Champions League and was named the 2008 Ballon d'Or winner.
But the Portugal international insists the Special One is the best coach in the world, and will prove it by leading Real Madrid to a historic tenth Champions League trophy this season.
"Jose is the world's best coach, he's number one," said Ronaldo in The Sun. "It's so great to work with him because I'm a person who likes to win, compete - and who hates losing!"
The 27-year-old has enjoyed a remarkably successful spell since leaving Manchester United for Real Madrid in 2009.
The Portuguese star won his first La Liga title last season, hitting 46 league goals in the process, and is in contention to win his second Ballon d'Or this year, although he faces stiff competition from three-time winner Lionel Messi.
Ronaldo returns to Manchester this evening to take on Manchester City, with Real Madrid all but qualified from Group D. The Real Madrid superstar hit the winner between the two sides in September, and is averaging better than a goal a game this term - with 19 goals in 18 games.
The La Liga champions can effectively clinch qualification for the knockout rounds with victory over Mancini's Manchester City.
Manchester United lost 1-0 to Galatasaray in Turkey last night, but Sir Alex Ferguson's side have already qualified for the next stage, and the Old Trafford club could afford to rest a number of their big names.