The Portuguese boss is under considerable pressure at Stamford Bridge following a woeful start to the Premier League and Calderon, who is still well connected at the Bernabeu, believes current president Florentino Perez would welcome him back if it doesn't work out with Rafa Benitez.
The 64-year-old said Perez even tried to get Mourinho to return last summer but settled for the former Liverpool manager as their fourth choice option.
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He also claimed Los Blancos want to sign Blues superstar Eden Hazard.
As per the Mirror, Calderon told beIN Sports: "If he is not anymore in Chelsea, I think Perez would be really willing to bring him back to Real Madrid.
"He (Perez) was trying to do that this season. He couldn't because Mourinho didn't like to come. He said he didn't like that for various reasons and then Perez went to sign (Joachim) Low, the German that is coaching the national team, then Klopp and finally Benitez.
“The truth is that Benitez was the fourth option for Real Madrid. I think Perez is still trying to bring (Mourinho) back here. He really likes him.
"I don't rule out that (Mourinho will be back at Real Madrid). If he is not anymore at Chelsea and Benitez is not doing well at the end of the season here, I don't rule out he's going to be back here. The president is really looking for that.”
In regards to Hazard, he added:"They are looking at him and, as far as I know, he has not said no. We will wait and see.”
Reports have suggested that Mourinho could be sacked by Chelsea if they fail to beat Liverpool at the weekend.
The west London club were knocked out of the Capital One Cup by Stoke City in midweek and their early slump shows no signs of improving.
On the other hand, Real Madrid have made a strong start to the season and sit top of La Liga under the stewardship of Benitez.
They are level on points with Barcelona and face the Catalan club in the first El Clasico of the season on November 21.
Will Jose Mourinho be sacked by Chelsea before the end of the season? Have your say in the comments section below
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