For how long is unknown.
"He's going to miss some time, there's no doubt about that," head coach Bill O'Brien said.
The Pro Bowl running back suffered a groin injury on Monday evening at practice. O'Brien said the organization had "no idea how much time he'll miss."
In 2014, Foster gained 1,246 yards in 13 games. He averaged 4.8 yards per carry and scored a combined 13 touchdowns on the ground and through the air. Behind him on the depth chart are Alfred Blue, Jonathan Grimes, Chris Polk and Kenny Hilliard.