Ibrahimovic has not played since suffering a career-threatening knee ligament injury in United’s Europa League quarter-final second leg match against Anderlecht at Old Trafford in April.
“He (Zlatan) is very strong but soccer is still a combative sport. As a doctor, of course I want to see him return as slow as possible, only when he is fully fit for the game,” Fu told the South China Morning Post.
“There have been many cases of a player returning prematurely with bad consequences.”
United manager Jose Mourinho is keen on leaving the 35-year-old striker out of first-team plans until January though he included him in the squad for the Champions League group stage which runs from September to December.
“I have no worry about his injury as it always takes time to fully recover,” Fu added.
“In fact the EPL (Premier League) 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.”
Ibrahimovic finished as the club’s top scorer last season with 28 goals in 46 appearances.