Redskins' running back Clinton Portis didn't practice on Monday because of a sprained knee and is listed as "50-50" for Sunday's game against the Cowboys. Portis bruised his knee on the final play of the first quarter of last week's 23-6 loss to the Steelers and is second in the league with 995 rushing yards. "He's questionable," Coach Jim Zorn said. "I'd say there's a 50-50 chance. I'm hoping that he'll be even better than that. Another day of rest, and then we'll see how he comes in on Wednesday. ... We've got to get the pain out of the knee and see how he progresses along."