The Brazil-born Spanish striker has been out of action for two weeks with a hamstring injury as well as a virus which forced him to hospital earlier this week.
Costa's woes suggest he is likely to miss Sunday's trip to Old Trafford but Mourinho was hopeful that he could at least play some part.
The Blues manager also indicated that John Obi Mikel and Ramires could also be included after being sidelined in recent weeks.
"There is a chance, he has a little chance. Diego has a little chance, the same as Ramires and Mikel," said Mourinho.
"Everything happened (to Costa). He was obviously injured - that was hamstring. He had to go to hospital with a viral situation that we didn't manage to resolve without being in hospital over one night - that was before (the midweek Champions League win over) Maribor.
"Against Maribor he wouldn't have been ready from the injury, no chance. But being ill didn't help the recovery process because we didn't have him at Cobham (training ground). Medical staff had to go to his house because we didn't want to bring him here with a viral situation.
"He trained individually, not yet with us."
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