ALAMEDA, Calif. (AP) -- Stefen Wisniewski walked slowly through the Raiders locker room, a thick black brace around his right knee. He paused at his stall briefly, donned a black hoodie then moved back out the way he came.
For only the second time in three seasons, Oakland's starting center is facing a Sunday with no football. Wisniewski suffered a knee sprain in last week's loss to the Washington Redskins and hasn't practiced since.
It's another blow to the Raiders offensive line, which could go into Sunday's game against San Diego with only one of its projected starters still in place.
''It's definitely a challenge,'' said five-time Pro Bowl offensive lineman Andre Gurode, who will start if Wisniewski is unable to play against the Chargers. ''You just try to get with everybody, make sure everybody's on the same page and make sure everybody knows what we have to do. That's what we're doing.''
Since losing left tackle Jared Veldheer to a triceps injury in training camp, Oakland has scrambled to keep the same unit on the field for longer than a week.
Tony Pashos was signed just before the start of the regular season to replace Barnes at right tackle. Pashos has started all four games but has been limited in practice this week with a groin injury.
Right guard Mike Brisiel is the only player still playing in his original position, while Gurode and Lucas Nix have split time at left guard.
Wisniewski had been one of the few constants as well before injuring his knee. The 48th player taken in the 2011 draft, Wisniewski has played in 35 games in his two-plus seasons with the Raiders. The only other game he missed was the season opener last year.
Although the 6-foot-3, 307-pound center has not practiced this week and is still a longshot to play against the Chargers, the Raiders have not ruled him out.
''He's made some improvement and we'll see if he's able to practice (Friday),'' coach Dennis Allen said. ''We'll see if he'll be able to go.''
Oakland's entire offense has been devastated by injuries.
Running back Darren McFadden remains sidelined with a sore hamstring, while fullback Marcel Reece has been limited in practice with a knee injury. David Ausberry, the projected starting tight end, never played a down in the regular season and was placed on injured reserve in late September.
Quarterback Terrelle Pryor was in that group with a concussion but has since recovered and will be back in the starting lineup this week.
No group has been hit quite as hard as the offensive line.
If Wisniewski can't play, Gurode - who went to five straight Pro Bowls with Dallas from 2006-10 - will make his first start at center since the final game of the 2010 season. He spent 2011 with Baltimore at left guard, and was with Chicago last season but did not play.
''I don't know if it's going to change what we can and can't do,'' Allen said. ''Obviously, you want to have Wiz in there. I think he's a really good football player and does a great job for us in there and handles a lot of the communication for us. That'll be a little bit of an adjustment if he's not able to go.
''If he's not, I feel confident that Andre Gurode can go in there and do the job. He's played center in this league for a long time and been a good player in this league for a long time.''
Notes: FS Charles Woodson returned to practice after skipping Wednesday's workout for non-football reasons. ... DE Jason Hunter (quad), DT Stacy McGee (shoulder) and OL Menelik Watson (knee) were limited. ... Allen insists he's not concerned about Sebastian Janikowski's struggles. Janikowski has missed three field goal attempts in four games. He had just three misses for all of 2012.
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