Zlatan Was brought in by Manchester United on a free transfer after his contract got over with Ligue 1 champions Paris Saint-Germain.
The former Swedish international who has already 12 goals English Premier League goals in 17 matches is in a sublime form even at the age of 35 years.
He joined the Red Devils on a one-year contract. But Mourinho now suggests that he is confident that the striker will stay back for one more season.
Speaking to media, the Portuguese manager said: "I'm not really surprised [by his form] because he's a very intelligent guy, a very proud man. For him to decide to come to Manchester United, the Premier League, the most difficult league in the world for a striker - it's because he knows he can do it.
"When we contacted him and he said yes, I was sure he was not coming here to leave the Premier League without proof, to leave failing at Manchester United - no way.
"So when such a guy decided to come, I was completely clear that he would be ready and he's ready for more next season. He'll be here again."
Manchester United defeated Sunderland last night, December 26 at Old Trafford with Zlatan scoring and assisting another.