Ronaldo left Manchester United in 2009 for a world record £80 million (A$157m) transfer to Madrid, but Calderon, president of the Spanish club at the time, said Ferguson wanted a different outcome.
"It was a difficult negotiation with Manchester United because obviously they did not want to lose the player," Calderon said to Al Mayadeen.
"But he was very clear about the commitment he made with me. He wanted to come to Real Madrid. The opportunity I offered him was very important.
"Ferguson did not want him to leave to us because he does not really like Real Madrid, which has been a rival and a team that has achieved everything he would have liked to win.
"Although Manchester United has won many titles, Real Madrid has won many more. And he [Ferguson] offered it [the deal] to Barcelona.
"Barcelona were obviously delighted with that opportunity, but Cristiano Ronaldo was very clear.
"He said that he had signed a commitment with Ramón Calderón to go to Real Madrid and 'I will not change that'. So that was it.
"So that there was no doubt we signed a clause so that if either party breached their commitment, they had to pay €30 million (A$50m) to the other party.
"That was a problem that produced a confrontation or, let's say, a dislike of the player with the current president (of Real Madrid, Florentino Pérez).
Ronaldo went on to become one of Madrid's greatest ever players - scoring an incredible 451 goals in 438 appearances across nine seasons.
And when the Portugal legend left Madrid for Juventus in 2018 as a 33-year-old, it was for €100 million (A$172m).
