12/26/2012 01:21 EST | Updated 02/25/2013 05:12 EST

Man United striker Wayne Rooney facing 2-3 weeks out after sustaining knee injury in training

MANCHESTER, England - Manchester United striker Wayne Rooney faces spending up to three weeks out with a knee injury.

Manager Alex Ferguson says the injury was sustained while the player tried to hit a volley toward the end of training on Tuesday.

Ferguson says Rooney "strained a ligament behind the knee. It's unfortunate, and he could be out for two to three weeks."

The England international missed United's 4-3 win over Newcastle on Wednesday.

Ferguson didn't specify which knee was injured.