The Portugal international worked with Sir Alex during his spell at Old Trafford from 2003 until 2009 and has not forgotten about his former mentor.
"He is the coach who taught me how to be a footballer. I arrived in Manchester when I was just 18 remember," Ronaldo told Times of India.
"He directed my career in the best possible way and for me he’s one of the most important people in the world of football. I have a great relationship with him and it will be good to see him again.
"Ferguson and Jose Mourinho are both great managers, both experienced, and both always want to win everything they can. That’s why they have been champions so many times."
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The prolific attacker then went on to discuss Tuesday's return to Old Trafford and stressed that, even though United still hold a special place in his heart, he is desperate to come out victorious in the second leg of their Champions League round of 16 tie.
He added: "Manchester was my home and is still in my heart. I love the place. You never forget when people treat you right. You never forget the people who work there and the fans.
"So I’m very happy to return to Manchester. It’s going to be special but of course I am going there to try and win with Real.
"More than anyone I know how difficult it is going to be, because I know how good United are and they have an amazing manager in Sir Alex Ferguson. I have a feeling we will win, because in my mind Real Madrid are the better team."