The experienced goalkeeper has returned to training following a spell on the sidelines with a finger injury.
However, despite the fact that he will soon be available for selection again, Mourinho has revealed that Diego Lopez will continue between the posts for now.
"[Casillas] is training well. He needs to carry on doing so and wait for his opportunity," the Portuguese coach told reporters.
"There should be no law that says any particular player should play. No-one should play for what they have won in the past."
Several recent reports have suggested that the working relationship between Mourinho and Casillas has become seriously strained.