CINCINNATI — Clinton Portis didn't even want to be on the field for the first preseason game. Now, the dependable running back isn't sure if he can be on the field when it counts.

The Washington Redskins' revamped offense took a significant jolt Sunday night when Portis partially dislocated his left shoulder during a 19-3 loss to the Cincinnati Bengals, leaving him sidelined indefinitely.

"Right now, it's tough to say," coach Joe Gibbs said. "Obviously, it's going to be a while."

Portis ran for a club-record 1,516 yards last season, when Washington made the playoffs as a wild-card team, and was counted on to steady an offense retooled by assistant coach Al Saunders in the offseason.

Instead, Washington is wondering how long it will be without its best running back — something Portis can't comprehend.

Portis opened the game with an 8-yard carry, then blocked for Mark Brunell's passes. When Brunell's sixth throw was intercepted by cornerback Keiwan Ratliff, Portis ran him down and reached to make the tackle.

His left arm was extended when he hit Ratliff, momentarily knocking the bone part of the way out of the shoulder socket.

"After that 8-yard run, I was like, 'Get me out of that game,"' Portis said. "That's what I was thinking. It's football. It can happen to anyone. It happened to me."

Standard treatment involves rest and strengthening exercises. Portis had the left arm in a blue sling after the game, when he lobbied for regulars to play less in the preseason.

"For whoever's watching: Let's get rid of some of these games," Portis said. "Four games is ridiculous. Then you play a 16-game season and the playoffs behind that."

Gibbs planned to keep Portis and his other starters in the game for only a short time.

Without Portis, the running game will depend upon backup Ladell Betts, who ran for 338 yards last season.