The Primera Liga champions have long been interested in the Portugal winger who has had a phenomenal season - with his 41 goals this campaign firing United to the Premier League title and the Champions League final.

Reports in Spain have linked Real with a £100million bid for Ronaldo but Calderon knows that even that amount might not persuade United to part company with the PFA and Football Writers' player of the year.

"There are many fans who would love to see Cristiano Ronaldo play in the Bernabeu," Calderon told Spanish TV programme 'Va de Futbol'.

"It's very difficult because he has a contract with a club that don't want to sell him.

"It's almost impossible, but not completely impossible because things can change between now and when the transfer window shuts."

Calderon was full of smiles at a successful season, which saw his team win their second successive Primera Liga crown - an occurrence that last took place 18 years ago.

And though he remained coy on whether Real would try to buy AC Milan star and world player of the year Kaka, he insisted that they are already planning for the summer with renewing Robinho's contract top of his list.

"I don't know if there will be the possibility of signing Kaka if Milan don't reach the Champions League," he continued.

"But they are only a buying club.

"We have to renew Robinho's contract because it's now three years old."