Rooney's last game was the 1-1 draw with Swansea City, he was expected to be missing from action for around two weeks at the time, but at the moment he has not been able to return to training and that will certainly rule him out of the West Ham FA Cup tie and the visit of Liverpool to Old Trafford next week.
But Ferguson insists that not having one of his major stars available will not affect the way they are playing although he does admit he could have done without the injury coming at such a crucial time of the season.
He said to reporters: "Wayne Rooney is still injured. We're surprised it's longer than we thought. We expected him back training but he's not. It's nothing serious but if looks as if he'll out for another two weeks or so.
"He won't be fit for that I don't think. It's nothing serious, he just got clipped behind the knee, and we sent him for a scan but nothing really shows on the scan and he's still feeling it.
"Hopefully two weeks will sort it but it's a loss and although we're in great form you want your best players available for the big games coming up.
"We've got West Ham, Liverpool and Tottenham the week after that and the FA Cup hopefully after that so it's a tough period and you want your best squad available. We've not had that all season anyway so it's not as if we can't cope, we will."