Calderon: Mourinho couldn't handle pressure
Mourinho was in charge for three seasons at Santiago Bernabeu, where he won La Liga in 2011-12, the 2011 Copa del Rey and the Supercopa de Espana.
A UEFA Champions League victory eluded him, however, as Real crashed out in the semi-finals three seasons in a row under Mourinho, with the club winning the tournament in 2014-15 during Carlo Ancelotti's first campaign.
Mourinho's Real reign was also marred with controversy, including poking then-Barca assistant Tito Vilanova in the eye, being sent off in the Copa del Rey final against Atletico Madrid and amid reports of disharmony within the squad.
The Portuguese tactician returned to Chelsea in 2013 and Calderon thinks his Real departure was more down to his inability to deal with the pressure of one of the biggest jobs in world football.
"To be a manager of Real Madrid is really, really difficult," Calderon told BBC World Service. "See what happened to Mourinho.
"He is someone who is used to coping with pressure and he couldn't.
"When Mourinho left, things were in a really bad situation. He had to leave the club after three years of a lot of problems, a lot of confrontations."
Ancelotti replaced Mourinho and delivered Real the 'Decima' in the Champions League last season, something that has impressed Calderon.
"To be here more than two, three years is really a big task," he added.
"I think he [Ancelotti] has done a very good job, not only because he won the Champions League but because things are calm, relaxed and everything is smooth."