The 28-year-old played under the Scottish manager while at Manchester United from 2003 until 2009.
"He is the coach who taught me how to be a footballer," he told the Times of India. "I arrived in Manchester when I was just 18 remember.
"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."
Ronaldo left United for Madrid in the summer of 2009.