The 32-year-old has lost his Chelsea place to Thibaut Courtois after Mourinho installed the Belgian as his no.1 against Burnley.
The Blues boss has previously insisted that Courtois is not his no.1 for the rest of the season and that Cech can fight his was back into the starting XI.
However, he did admit that the 22-year-old will start against Leicester City on Saturday, leaving Cech on the bench for now.
And Mourinho has acknowledged that, despite continuing to work hard during training, the Czech is not happy with his current situation.
"[He is a] top professional, working hard as always, behaving as always, being a group man as always. Being a Chelsea person as always," Mourinho told reporters at a pre-match press conference on Friday.
"Is he totally happy? I don't believe [so]. But it's not him, it's everyone that didn't start the game [against Burnley].
"I think this period is hard for them and for me because there is only one match per week. Some are playing more and some don't.
"But September, everyone will be playing with rotation and resting, so it will be an easy period for them [the players] and for me."
Whether that means Cech will leave Stamford Bridge this summer is yet unknown, although Mourinho could consider playing him in European and cup competitions.