The Sun says shocked medics said the horrific gash on Rooney’s right leg was among the worst of that type.
The cut went through to the bone injuring the muscle in his thigh.
Boss Alex Ferguson had thought it would only sideline Rooney, 26, for a month.
Rooney needed 10 stitches to pull his skin together.
Another long weaving stitch will have been inserted inside his leg the length of the cut to repair the damage caused when Fulham striker Hugo Rodellega inadvertently stood on him.