Manchester United manager Ferguson reckons Real got a bargain and the 27-year-old striker is now worth a phenomenal £800m.
"He's right. I have to agree with him," Ronaldo told The Sun. "No, I'm joking. These are just opinions.
"But I have to say thank you because when people say nice things about you it always motivates you.
"When I arrived at Manchester United I was 18 years old and Sir Alex Ferguson was like a father to me. He taught me many things. I worked with him for six years and he is a great human, a great coach.
"Sir Alex and Jose Mourinho are the two best coaches in the world.
"My cycle with Sir Alex has ended, so it is great to work with Jose Mourinho because, at the moment, he is No 1."