Current president Florentino Perez has been linked with potential moves for Jose Mourinho to replace manager Manuel Pellegrini and Manchester United striker Rooney.
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"Sometimes it's a point of money and if there is a proposal maybe there will be a deal.
"You have to take into account that the most important thing is what a player wants to do.
"Ronaldo was a good signing. He is one of the best. He is a professional, a real professional and he is doing a really good job.
"I don't know if it is possible to spend again another 100 or 80 million more euros. I imagine in that case you (Manchester United) would have to sell."
Asked on BBC Radio Five Live's Sportsweek programme if Ronaldo regretted his move to Madrid, Calderon added: "I don't think so.
"He did what he wanted to do, he came to a big club. The idea was to win everything but you can't buy everything with money.
"Even though you think you've got lot of very good players together, that's not the same as having a good team."