When Zlatan Ibrahimovic suffered a serious knee injury playing for Manchester United against Anderlecht in April, there were fears for his career.

It was believed that the injury could rule the 36-year-old out for 12 months and, with his contract set to expire at the end of last season, his future was in doubt.

But Zlatan was never going to be ruled out for a year and immediately showed he was determined to bounce back as quick as possible. That determination saw United reward him with a new deal and, seven months after suffering his injury, he was back playing once again.

And in typical Zlatan style, the Swede explained how he had bounced back so quickly.

"I told you, lions don’t recover like humans. That I have now proved, rather than just saying it," he said back in November.

But since making his long-awaited return against Newcastle last month, things haven’t exactly gone to plan for Ibrahimovic.

He’s still yet to start a match and has been restricted to five substitute appearances, making very little impact.

Man Utd are concerned

And now there are serious concerns about him.

According to The Sun, staff at Old Trafford “fear Zlatan Ibrahimovic may never be the same player” following his horror knee injury.

Mourinho has already had to leave the striker out of two matches in order for him to return to the gym and build up strength in his knee.

And it seems he may have rushed his recovery and it could have disastrous results for the remainder of his career.

Mourinho could sign another striker

And because of doubts over Zlatan and Romelu Lukaku struggling to maintain his fast start to his United career, Mourinho could dip into the transfer market in January for another striker.

That could potentially be Antoine Griezmann after Atletico Madrid manager Diego Simone admitted he could leave the club in the near future.

"Of course Griezmann will be able to leave at some point, the same way (Diego) Costa and Arda Turan were allowed to leave," Simeone told l'Equipe.

"I love my players a lot and I love to see them grow. I am not ungrateful.

"If a player comes to me and says: 'Coach, I have a once in a lifetime chance to play for a certain team, I want to leave'.

"If he did all he could for me as Griezmann does, I'll say it's no problem. I know that he needs to grow."