The Blues boss says the £32 million striker still has a chance of playing against Everton.
On Costa, the 'Special One' says the Blues have yet to make a decision on whether to select him against the Toffees.
The Spain striker, signed in the summer from Atletico Madrid for £32 million, was initially feared to be out for several weeks.
However, Mourinho has confirmed he could still make the bench at Everton.
"At this moment, I can't say much. We are trying everything for him to play tomorrow. He didn't train for the last two days. Today we must make a decision to select him or not," Mourinho told reporters at a pre-match press conference.
"He has to try a light training session to see if the reaction is positive. If the reaction is positive, we take him to Everton to play, to be on the bench. Let's see. If the reaction is not positive today, obviously we don't select him."
On Torres, meanwhile, Mourinho explained that the Spaniard could well be on his way out of Stamford Bridge this summer. That, though, would leave the club 'in trouble.'
"If that [Torres leaving] happens in the last hour of the market, we are in trouble because, until this moment, we are doing nothing because our belief is that the market is closed for us," the Portuguese coach explained.
"Our belief, for a long, long time, is that the market is closed. We have our squad, we like our squad. It's not the perfect one because no squad is the perfect one but it is a squad we like."
Mourinho also confirmed that, 'due to rules,' the Blues must sell a non-homegrown player before the transfer window, though he refused to entertain suggestions as to whom it might be.
Mourinho's comments suggested the player would not be Torres, as he would be involved in a separate deal, with the club needing to replace him if he left - likely with another non-homegrown striker.