Rooney was kept in hospital on Saturday night, and was operated on Sunday . A surgeon sewed up the deep gash caused by Hugo Rodallega 's boot on his thigh as he slid in to block a shot.
United manager Sir Alex Ferguson  had envisaged that Rooney would be missing for four weeks, ruling him out of England's World Cup qualifiers against Moldova and Ukraine next month.
However, medical opinion suggests the severity of the wound could mean a six-week absence.
Rooney had one long, weaving stitch inside his thigh and then another 10 outside to pull the skin together, The Daily Express reports.
Although, Ferguson has cleared Rodallega of any blame, one suggestion as to why the cut was so deep and wide was because the Fulham striker was wearing bladed boots.
Ironically, Ferguson banned United players from wearing bladed boots some years ago, believing they caused too many injuries, with metatarsal bones particularly vulnerable.
After Saturday's game, Ferguson said: "It was an accident. He followed through after his shot. But it's a bad one and it looks like he will be out for four weeks." (ANI )