Manchester United manager Sir Alex Ferguson has admitted that Wayne Rooney could be out for longer than the three weeks initially expected.The 25-year-old striker is currently on holiday as he recovers from the ankle injury he picked up in training.Rooney recently signed a new five-year deal to stay at Old Trafford days after he said he wanted to leave the club.Asked if three weeks was still the prognosis for his return, Ferguson said: "I think it may be longer."Ferguson added: "There is no recovery, it is just rest."Before he went away we did his remedial in terms of what we could do at the time. Thereafter, rest - we're quite happy with that."Rooney, who has been recuperating while on holiday in Dubai with his wife Coleen, has missed United's last three matches, his last appearance being as a late substitute in the 2-2 draw with West Brom on 16 October.The England striker has struggled for form this season and has scored only one Premier League goal, a penalty in the 3-0 win over West Ham in August.Rooney had been targeting a return to action for the derby clash with Manchester City at Eastlands on 10 November.That fixture would have pitted Rooney against a side that was widely tipped to bid for his signature after the former Everton player stated his desire to leave.However Rooney completed a remarkable U-turn two days later by committing himself to staying with the Red Devils, signing an improved contract that could keep him at Old Trafford for the next five years.Source: BBC