Arlington, TX -- (Sports Network) - Washington Redskins running back Ladell Betts suffered a knee injury in the first quarter of Sunday's game against the Cowboys and did not return.

The injury was deemed "significant" after Betts was tackled by Cowboys linebacker Bradie James on Washington's second drive on the game.

Betts started his second straight game in place of the injured Clinton Portis (concussion). He ran for 114 yards and a touchdown on 26 carries in a 27-17 win over Denver last week.

Rock Cartwright was a serviceable replacement on Sunday, leading the Redskins in rushing and receiving with 67 yards on 13 carries and seven catches for 73 yards in the tough 7-6 loss.