An already thin secondary sustained another injury yesterday afternoon when safety Clarence Vaughn sprained his left knee. He was helped off the field and it appears he probably will not play Sunday against the Dallas Cowboys at RFK Stadium.

Cornerback Alvoid Mays didn't practice yesterday after injuring his right knee on Wednesday. Mays was walking very gingerly and might have trouble playing Sunday.

The Redskins are still hopeful Mays can play against the Cowboys, but with their secondary down to six healthy bodies, General Manager Charley Casserly alerted veteran cornerback Wayne Davis that he might be needed.

Davis was released in the final round of roster cuts and has the advantage of knowing the system.

This latest injury continues a bad run of luck for Vaughn, who severely bruised a shoulder late in training camp. Just when he was getting over that, he has another problem.

Mays also was released in the final cutdown, but was brought back after clearing waivers. He said he hoped to play this week, but added: "I just don't know. I twisted it pretty good and it doesn't feel good right now. I'm going to try to stay optimistic, but it's sore today."

Coach Joe Gibbs said that if Mays can't play, the Redskins might be forced to rearrange their personnel in the secondary. With Darrell Green, Martin Mayhew and Brian Davis the only healthy cornerbacks, a safety, probably Alvin Walton, might have to play corner in some nickle situations.

Wayne Davis also could be asked to play some safety if Vaughn can't play.

Clark, Coleman Hamstrung

Receiver Gary Clark and linebacker Monte Coleman missed a second straight day of practice with pulled hamstrings. The Redskins hope both will be able to play Sunday, but might not know until game time. If Coleman can't play, rookie Andre Collins might play the entire game at outside linebacker. Clark likely will start and play at less than 100 percent.

"I've played with worse," he said. Gibbs also has Ricky Sanders and Walter Stanley available.

Brandes Has Special Ability

After leading the Indianapolis Colts in special teams tackles last season, John Brandes signed with the Redskins as a Plan B free agent and announced he'd lead his new team in special teams tackles as well.

After two weeks, he's doing that: His five tackles are one more than Mays and Brian Mitchell have. Brandes said if he sometimes makes more plays, it may be because he works at it.

He won a spot at tight end, not because he was better than Ken Whisenhunt or Mike Tice, but because he could do so many other things -- snap for field goals, play special teams and play tight end.

"During the week, I spend 45 minutes to an hour studying special teams films," he said. "I try to see where people are going to try to get to me and what their idea is. I feel like if I'm going one-on-one with someone, I'm not going to get blocked. I have enough faith in my athletic ability to believe that."

Brandes said he likes it for another reasons. "There's nothing like special teams," he said. "It's the one part of the game where you can go out and play with reckless abandon and be rewarded for it."