Last month, departing manager Sir Alex Ferguson revealed he had rejected a transfer request from the England international. Sorting the 27-year-old's future is one of the key things for new boss David Moyes to address but van Nistelrooy - who left Old Trafford for Real Madrid in 2006 - expects it will ultimately be the player's decision.
"It is a matter of how he feels. If he feels he is committed to the club I think there is an opening," said the Dutchman.
"If he says there isn't I don't think there is a future for him but it is up to him. I think the fans would love him to stay but it depends on the commitment.
"If he is fully here everyone loves him but when he is not fully committed it is probably better to move on."
Former Red Devils defender Henning Berg also thinks Rooney will have final say on the matter, although he does not expect United to give in easily.
"It is up to Wayne Rooney. If he is 100 per cent committed and wants to play and that is everything he has to go for he has the talent and the qualities to play a big part at this club," he said after a United v Real Madrid legends game in aid of the Manchester United Foundation.
"I think David Moyes and Rooney have to talk about that and if Rooney feels it is not 100 per cent for him then maybe things will change.
"I don't know too much about the history (of Rooney's transfer requests) but with David Moyes coming in they have to sit down and talk about it - but ultimately Wayne has to see what he feels.
"He is still under contract so I think the club is still in a good position."
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- David Moyes
- Real Madrid
- Wayne Rooney