After three seasons on loan at Atletico Madrid, the 22-year-old Belgium goalkeeper has returned to Stamford Bridge and taken the place Cech has occupied for a decade.
Courtois has two years remaining on the contract he signed when moving from Genk in July 2011, with an extension close.
"It's not yet signed," Courtois told Sky Sports.
"I am here with the national team so it is difficult, but when I am back at Chelsea I will probably sign the new contract."
Courtois started the first three Barclays Premier League games of the season ahead of Cech.
It is a situation reminiscent of when Cech was installed as number one ahead of the established Carlo Cudicini after his signing from Rennes in June 2004.
Mourinho's decision led to suggestions Cech would leave, but the Czech Republic goalkeeper remains after Monday's closure of the summer transfer window despite reported interest from Paris St Germain and Real Madrid.
Courtois added: "We don't talk about the situation, but of course I know he has played 10 years at Chelsea and that now I am playing and for him it's not the nicest situation
But that is the decision of the board and the trainer.
"He is working hard in training to be ready when I cannot play or I am maybe not playing well
We work well together.
"Of course as a professional and a winner you always want to play every game, so we will see what the decision is of the coach.
"But of course I am a professional player and I want to play every game that is possible."
Source : PA
Source: PA