Perez admits Mourinho struggled to understand the reaction of fans at times.
"Mourinho has taken a while to understand what Real Madrid is about. He was surprised by the club, the people and the fact that the fans whistle at the players and at him," Perez stated at the club's Assembly.
"He emphasised the fact that he had been at several clubs, in Portugal, Italy and England, but I told him that this is Real Madrid. A truly unique club.
"The club's expectations are much higher than those of other clubs and if things don't go to plan on the pitch, the fans start to whistle. Some players who have come here have failed to understand this concept."