The Spain striker, who has netted nine times so far this season, has been struggling with a hamstring injury as well as illness.
But Mourinho is confident his star man will return to action in the west London derby at Stamford Bridge.
Chelsea loanee Ryan Bertrand is eyeing a permanent move away from the club.
The 25-year-old is currently on-loan at Southampton and has impressed during the early period of the season.
And Bertrand, who started in Chelsea’s 2012 Champions League triumph over Bayern Munich, is certainly not against the idea of making the switch to the south-coast a permanent one.
”It is one of those things where I’ve got to wait and see, but, for me, there’s no reason why not,” he said.
”There is a good base to the club, we’re pulling in the right direction. We have fantastic fans, fantastic players, a fantastic manager and coaching staff.
”It has been a good experience for me so far, so I don’t see why not.”