Ibrahimovic scored 28 goals in his maiden campaign in English football before suffering a serious knee injury in the Europa League quarter-final with Anderlecht in April.
The 36-year-old striker is making impressive progress in his recovery from knee ligament damage after being rewarded with a contract until the end of the season. It was initially thought he would not return until the New Year.
But hard rehab work in the gym means he could face CSKA Moscow in the Champions League on December 5, according to media reports.
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"Zlatan is here. He's working here and under our control," said Mourinho.
Manchester United's Zlatan Ibrahimovic celebrates at the end of the match with Jose Mourinho
Image credit: Reuters
"He's working as you would expect - so, so, so hard. But he's not going to be back in the next week or the next couple of weeks. Let him take his time and be back when everybody feels is the right moment.
"Do I believe he'll be back in 2017? Yes, I do. But it's just a feeling."
Former United striker Andy Cole believes the Swede could be back in action in December.
"I had a chat with Zlatan when he was in the gym the other day," said Cole. "I think he is looking forward to coming back, most probably in December or January time."
Ibrahimovic scored in both the EFL Cup and Community Shield successes at Wembley last year.
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