The Swede has suffered a setback in his recovery from April knee surgery.
Mourinho said the Swede wouldn't be rushed back into action but is expected to return to training at the end of the month - depending on how he feels.
“Zlatan is injured, or is not totally happy with his condition," said Mourinho.
"He fought like a tiger, like he likes to say, to be back, which he did.
"He was starting having minutes here and there, he had a start, he had 60 minutes of one game and started another one, and had 45 [minutes], and he was not happy with his feelings.
“He consulted other doctors and other opinions, and we all made the decision to stop treatment. When he's feeling really good, he can come back to work.
"The date for him to be back to training with the team was around the end of January or beginning of February, so let's hope his feelings are better and we have him as soon as possible."