Former Real Madrid president Ramon Calderon has told talkSPORT that the European champions would be making a "big mistake" if they let Cristiano Ronaldo depart this summer.
Sources have told ESPN FC that Ronaldo, 32, wants to leave Madrid to play in another country rather than deal with what he sees as "persecution" in Spain after being accused of tax evasion totalling €14.7 million.
But Calderon -- who brokered the deal to sign the Portugal international from Manchester United in 2009 -- has urged Madrid to do all they can to keep hold of a player who he says cannot be replaced.
"It would be a big mistake if [president] Florentino Perez doesn't try to keep him with us," he said. "It took me a long time and a big effort to sign him when Man United didn't want to let him go. We have to keep him.
"I think he will stay. I hope so. It would be very bad business to sell him. It doesn't matter what we can get for him. There is no replacement for him. I don't see anybody in world football who can substitute for him."
Calderon concedes that Ronaldo is "strong-minded" when it comes to making decisions, as he learned first-hand when negotiating the deal to bring him to the Santiago Bernabeu eight years ago.
And with United, as well as Paris Saint-Germain, being linked with moves to sign Ronaldo, Calderon also acknowledged that the forward holds his former club in high esteem.
"He is very strong-minded and when he decides something he goes through with it," Calderon added. "The point now is whether he really has decided to leave.
"He likes Manchester United -- that is something we all know. One year before he was going to come [in 2008], he told me that he was really grateful to Manchester United, the fans, the people there, his teammates -- everything in the city."
Ronaldo is currently in Russia with Portugal for the Confederations Cup. He played in his country's 2-2 draw with Mexico on Sunday, but has not yet made any comment since news broke of his desire to leave Madrid.
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