Foster's left leg required an air cast and he exited after 10 minutes on the ground, according to Les Carpenter of The Washington Post. Head coach Jay Gruden, team president Bruce Allen, and defensive coordinator Greg Manusky all gathered around Foster as he was tended to be by the training staff.
The linebacker was apparently crying while being driven back to the Redskins' facility, according to Mike Garafolo of NFL Network.
Foster spent his first two NFL seasons with the San Francisco 49ers before being released last November following a domestic violence misdemeanor charge.
The Redskins then claimed Foster off waivers, and the charges against him were dropped in January. He was reinstated by the NFL after an investigation concluded he didn't violate the personal conduct policy.
The 25-year-old has been projected to start alongside Mason Foster in the center of the Redskins' defense.