The midfielder feels the ex-Real Madrid coach did not show the goalkeeper the respect his Spain team-mate deserved based on his performances
Casillas lost his starting berth to Diego Lopez under Mourinho after a hand injury and the Portuguese coach even went as far as to say that he should have changed goalkeepers at an earlier stage, much to the dismay of his Spain team-mate Xavi.
"I feel really bad for Iker because he doesn't deserve to be treated like that and I have seen how it has affected him. We've talked more than ever this year," the Barca playmaker told El Pais.
"It's not the fact that he hasn't played that's the problem; the worst thing is the comments. He hasn't been shown the respect he deserves.
"How can Mourinho say that his mistake was not signing a new goalkeeper two years earlier? I guess he doesn't remember, but Iker won them the Copa del Rey in Valencia with three amazing saves."
Mourinho left Madrid this summer for a return to Chelsea after three years in charge of los Blancos, with Carlo Ancelotti expected to be announced as the new Santiago Bernabeu coach soon.