Manchester United star Zlatan Ibrahimovic revealed his knee injury was worse than previously known, saying people would be shocked he returned.

The Swedish striker made his first appearance since April after coming off the bench in his side's 4-1 Premier League thrashing of Newcastle United on Saturday.

Ibrahimovic, 36, said his injury was far worse than previously known, although he preferred to keep the severity a secret.

"If people knew the real injury, they would be in shock that I was even playing. It was more than the knee but I will keep it personal – that's why I choose not to talk of it," he told UK newspapers.

"In my recovery I have not rushed anything. I have been out for six and half months. I have been following protocol and my schedule day by day.

"The only secret has been working hard. Those close to me know what I have been doing. I was working five, six hours a day."

Ibrahimovic scored 28 goals in all competitions for United last season before being released, only to sign a new one-year deal.

The veteran may be coming out of contract again, but he is unconcerned about his future.

"At the moment I am just thankful I can run and push it and play football again," Ibrahimovic said.

"I don't know what the future brings but what happens, happens. I am at the age where I can choose what I want to do.

"I don't sign five- or 10-year deals, I am just happy to be back playing and doing what I am good at.

"It's fantastic to be playing. Jose [Mourinho, United manager] said, 'Do whatever you want, I trust in you and you know what you have to do' so I was not worried.

"The contract is all paperwork and I do the physical work."