Ibrahimovic tore his anterior cruciate ligament against Anderlecht in April in the Europa League and signed a new deal at Old Trafford before missing the start of the season following an operation.
The 35-year-old is due back in training at the end of October, but the specialist who performed the surgery on his knee Dr Freddie Fu has urged United to be patient and give the striker as much recovery time as possible.
'He is very strong but soccer is still a combative sport', Fu told the 'South China Morning Post'. 'As a doctor, of course I want to see him return as slow as possible, only when he is fully fit for the game'.
'I have no worry about his injury as it always takes time to fully recover', Fu added. 'In fact, the EPL has just started and I am sure Manchester United would not need the player urgently for any crucial game either in the league or European competitions'.
Fu underlined Zlatan's strength and resilience: 'He has a very strong attitude. Even before the operation, he firmly believed he would come back in his soccer career and would not retire just because of the injury'.
But he still called for patience. 'There have been many cases of a player returning prematurely with bad consequences'.