The 33-year-old left Stamford Bridge this summer after 11 years, to join London rivals Arsenal in a deal worth around £10million.
Cech won four Premier League titles, four FA Cup triumphs and a Champions League victory with the Blues, but Mourinho believes he has been well replaced by Asmir Begovic.
“We don’t miss Petr,” the 52-year-old manager said.
“We’ve got a good keeper, the problem with Petr is not that we miss him because we have two excellent keepers.
“The problem with Petr is that an opponent is better than before.
“Thibaut and Asmir are two fantastic keepers. My club did very well by getting a keeper on time and not on the August 31″.
Courtois was sent off in Chelsea’s 2-2 draw with Swansea on Saturday and the club has appealed the decision, in a bid to have the goalkeeper available for this weekend’s trip to Manchester City.