Rooney picked up an ankle injury during the 2-2 draw against Bolton at the weekend. The striker is now set to miss the Premier League game against Sunderland and England's Euro 2012 qualifier against Montenegro.
"It will be two to three weeks. But it depends because Wayne has done quite well with his recovery from injury in the past."
Sir Alex also confirmed that Scholes will be out for a short time with a slight calf problem.
The good news is that Rio Ferdinand is set to return to the defence alongside Nemanja Vidic, for the first time this season. In six Premier League games without Ferdinand, the defence has conceded nine goals.
