Real president Florentino Perez has been linked with a bid for Rooney since last week's Champions League elimination.
Calderon told BBC Radio: "It seems that it's an obsession for the president to go for Rooney. I imagine Manchester United wouldn't like to lose a player like him.
"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.
"(Cristiano) 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."