Torres became Chelsea's record signing in 2011 when he joined from Liverpool for a fee of around Â£50million.
Mourinho has three strikers at his disposal this season following the recent arrival of Diego Costa and the return of Didier Drogba but the Chelsea boss insists each of the three are essential to his squad.
"We have a good squad," Mourinho said.
"The perfect squad would be with this 18 players, not 17 or 16, but rules are rules and we are working hard, even here, for not to have these kind of problems in the future.
"(We want) to have more English players in our squad which we are going to have in the future but in this moment we are still in the middle of this process.
"So at the moment we have to make a decision about one player not to be on that list."
And when asked whether this one player was Torres, the 51-year-old was quick to confirm the Spain international would be staying at Stamford Bridge:
"No. Three strikers is fundamental in a squad and we have three strikers; Fernando, Didier and Diego so one of them is not (going) for sure," he added.