Ibrahimovic tore his knee ligaments in Manchester United's Europa League quarter-final second leg against Anderlecht, and was ruled out for the rest of the season.
The 35-year-old had surgery at a medical facility in Pittsburgh last week, and the first pictures of him on crutches emerged on Monday.
His agent, Mino Raiola, says the surgery was so successful that Ibrahimovic will go back to the same place so his incredible knee can be examined for further medical research.
"Zlatan has started rehabilitation at the hospital. His knee is so strong that the doctors said they had never seen anything like it," Raiola told Expressen.se.
"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."
He added: "Zlatan is so strong that the doctor wants him back after his career to research on him.
"They work in the world's best research institutions for the knees and ligaments. They research a lot on the subject and that is why they are better than everyone else. And the doctors want Zlatan back to do research on him.
"So after Zlatan's career, we will go back and open him up again to do research on his ligaments."
Ibrahimovic has scored 28 goals in 46 appearances for United this season in all competitions. If Raiola is to be fully believed, Zlatan must be even more amazing than what the Swedish hitman thinks of himself. We didn't know it was possible.
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