A toe injury ended the 2015 season of Chargers backup running back Branden Olivver.
An Achilles tendon injury has jeopardized Oliver's 2016 season.
Oliver, the team's leading rusher in 2014, was carted off the Minnesota Vikings' new field Sunday after falling to the ground without being touched. Oliver had caught a screen pass from Kellen Clemens. When he attempted to push off his right foot, he fell to the synthetic turf and raised an arm in apparent pain.
Second-year running back Dreamius Smith replaced Oliver.
Rookie Kenneth Farrow, who is expected to run against the 49ers on Thursday, returned from an injury this past week and is also in contention for a backup job.