The Washington Redskins linebacker is believed to have suffered a torn ACL in his left knee, plus additional damage, sources told NFL Network Insider Ian Rapoport on Monday.
Rapoport added the injury is considered "major and significant." The linebacker will see specialists to determine the full extent of the injury.
Foster suffered the injury after getting pushed to the ground during the first day of Redskins OTAs on Monday, per multiple reporters at practice. Trainers, along with coach Jay Gruden and GM Bruce Allen, tended to the linebacker before he was carted off the field with an air cast on his leg, NFL Network's Mike Garafolo reported.
Gruden told reporters that Foster was going to undergo an MRI later Monday.
Foster's injury could sideline him for the entirety of the 2019 season. However, there is precedent for a player to return from this type of injury suffered at this time of the year.
Just last season, Los Angeles Chargers tight end Hunter Henry tore his ACL during OTAs on May 22. Henry missed the entirety of the regular season, but returned to practice on Dec. 17, took first-team reps the first week of January and returned to the starting lineup for L.A.'s Divisional Round loss to the New England Patriots on Jan. 13.
If Foster enjoys a similar recovery to Henry and the Redskins make a postseason run, perhaps the linebacker would be healthy enough to play late in the campaign. However, such a return is rare and unlikely.