NFL.com's Ian Rapoport reported Tuesday on "NFL Total Access" that doctors feared Ingram suffered a torn anterior cruciate ligament during the Chargers' organized team activities. The Chargers later confirmed the injury, which is to Ingram's left knee.
If Ingram has a complete tear of the ACL, he'll undergo surgery that likely will sideline him for the entire 2013 season.
Ingram, the 18th overall pick in the 2012 NFL Draft, is coming off an underwhelming rookie season in which he made only one start in 16 games. He finished with 16 tackles, one sack and one forced fumble.
Follow Dan Hanzus on Twitter @DanHanzus.