The NFC's other Pro Bowl running back, Adrian Peterson, could still be playing for the Vikings when the NFL holds its annual all-star game one week before Super Bowl XLIV.
Those factors could help the 49ers' Frank Gore, named first alternate to the NFC squad, land a spot in the game.
A back injury forced Jackson to miss the Rams' most recent game. An ankle injury has sidelined Williams twice in the Panthers' last four games. The nature of Jackson's injury -- a herniated disc -- could make it tougher to justify playing in what amounts to an exhibition game.