Michael Bush, off to a slow start after missing the first two games with a broken left thumb, handled the majority of reps in practice Thursday and will likely start against the Chargers.
McFadden's absence would be a blow to Oakland's sputtering offense. The former first-round draft pick is tied for third in the NFL with 392 yards rushing, 35 more than he had all last year. It's also the best start by an Oakland running back since LaMont Jordan had 424 yards after four games in 2007.
McFadden isn't the only Oakland player hurting.
Backup running back Michael Bennett (hamstring), left tackle Robert Gallery (hamstring), defensive tackle John Henderson (foot) and linebacker Thomas Howard ((knee) all sat out Wednesday's workout. Linebacker Quentin Groves (hamstring) was limited in practice but isn't expected to play much, if any, against San Diego.
Additionally, quarterback Bruce Gradkowski (shoulder) was limited while first-round pick Rolando McClain was excused for a second straight day due to personal issues, though the rookie linebacker will play against the Chargers.
The Raiders insist McFadden's injury isn't like the one that sidelined him early in training camp but coach Tom Cable said it was "very, very doubtful" that the third-year running back would play against San Diego.
Instead, Oakland will lean heavily on Bush, who has only 10 carries this season after leading the Raiders in rushing in 2009.
Bush's power running is in stark contrast to the quicker, slashing style of McFadden, though Cable doesn't think the Raiders will alter their offense much because of the change in the backfield.
"If you look at when Mike's played, it's been the same things," Cable said. "He runs more physical in the box maybe. You may not get as much play on the perimeter but you'll get it running downhill at the defense. [McFadden] has been very productive so we've got to find a way to get that same production but I think Michael's ready to take that load."
Neither Bush nor McFadden were made available to the media Thursday. McFadden didn't attend practice, either.
Rock Cartwright has taken only a handful of plays on offense for Oakland this year and will be Bush's backup if McFadden and Bennett are ruled out.
The Raiders could get a lift if Gallery is cleared to play. Gallery hasn't played in three weeks but Cable is apparently willing to start him if he practices Friday.
"The workout was good this morning, so if we can get some work out of him tomorrow we'll see what happens," Cable said. "If depends on how the work goes. If it looks erratic and all that, it's not worth doing that."
The Raiders failed to sell out for a 10th consecutive home game dating back to 2009, meaning the game will be blacked out in the Bay Area. ... Rookie OL Jared Veldheer took reps at center and left tackle with Oakland's first-team offense.