Casillas is out of the Real Madrid side after being displaced whilst injured by Diego Lopez.
“Not playing for Madrid may affect his chances with Spain at the Confederations Cup,” he told Marca.
“That he is not playing at Madrid is strange, but we must consider the circumstances. He had an injury, the club signed another ‘keeper and in the end he is doing well. The team makes the decisions and I cannot judge.
“We all know who Casillas is and what he means for Spanish football, but in the end it is Mourinho who has the last word. He is a great goalkeeper, but ultimately football is in streaks. In Spain there are others who are playing well.”
