The surgeons that operated on Zlatan Ibrahimovic's injured knee want to bring former Sweden captain back for further study.

“Zaltan’s knee is so strong that the doctors said they had never seen anything like it,” the Daily Mail quoted Manchester United striker’s agent Mino Raiola as saying ,

Ibrahimovic has been out of action since he suffered a cruciate knee ligament injury in United's 2-1 Europa League victory over Anderlecht last month.

The 35-year-old underwent surgery at a specialist facility based in Pittsburgh last week.

Raiola told Swedish publication Expressen.se: 'Zlatan has started rehabilitation at the hospital.

'His knee is so strong that the doctors said they had never seen anything like it.'

'He has a knee that it is almost impossible for a football player with a 20-year career to have. It was quite clean... there was no harm in it.'

Ibrahimovic's first season in the Premier League has been a huge success, with the veteran striker scoring 28 goals this season in all competitions including a brace in the EFL Cup final victory over Southampton.

The agent stated that Ibrahimovic would return to Pittsburgh for further testing when he decides to call an end to his stellar career.

'Zlatan is so strong that the doctor wants him back after his career to research on him,' he added.

Ibrahimovic, who arrived at Old Trafford from PSG last summer on a free transfer, is yet to agree an extension on his one-year United deal.