Fargas injured his groin midway through the second quarter when he tried to run a pass route down the sideline. Lined up against middle linebacker Pat Thomas, Fargas pulled up lame well before JaMarcus Russell's pass arrived, then fell to the ground holding the inside of his leg.
Fargas stayed on the ground for a few seconds, then limped to Oakland's sideline. He had 43 yards on nine carries before the injury after leading the Raiders with 97 yards on 18 carries against Denver last week.
In his place, McFadden ran for 164 yards and a touchdown in Oakland's 23-8 win.