The decision to drop captain Casillas for the first time in 10 years was the most controversial decision taken by Mourinho as coach of the club, provoking ire from fans.

“People have talked about it without knowing much of what may have happened in training or in the dressing room,” said Karpin, who spent over a decade in La Liga during his career.

“You have to know what has happened and why. No Coach does something that will harm himself or his team.

“Something must have happened. Nobody would just remove him from the team, he has been the best in the world in his position for the last five years. So, I am reluctant to speculate as to why.”