Coach Jim Zorn on Thursday ruled Portis out for Sunday's game at Dallas.
Portis has not been able to practice since he was injured in a helmet-to-helmet hit against the Atlanta Falcons.
Ladell Betts is set to start for Portis for the second consecutive week.
Zorn says defensive tackle Albert Haynesworth remains a game-time decision with a sprained left ankle. The coach says Haynesworth is "coming along" and that the ankle's swelling is starting to go down.