Santiago Solari is under pressure at the Bernabeu, after losing back-to-back games to Barcelona and being knocked out of the UEFA Champions League by Ajax within one week.
Mourinho, who left Real in 2013, disclosed last week that he was flattered to be linked with a return.
And Calderon has now said it is only a matter of time before it is official.
He told Sky Sports News: “I have no doubt Mourinho is the first option for the president. He’s been called in the last weeks.
“It was when Zinedine Zidane left, Mourinho was with Manchester United and he said it was not the right moment to come back, but maybe now he’s free.
“I think there will be many chances he will be on that bench next season.”
Asked about other potential candidates, he added: “Maybe Mauricio Pochettino, they are talking about him. But there will be many in the next days because fans can’t accept this situation.
“There’s been three or four months moaning now, lamenting and regretting what we did planning this team.”