Newton walked to the locker room with trainers after playing in three series against the New England Patriots. He was quickly ruled out for the remainder of the contest.
After the game, head coach Ron Rivera said Newton is "in a walking boot, and that's all I can tell you," according to Bill Voth of Panthers.com.
Newton's injury doesn't appear to be serious, a source told Ian Rapoport of NFL Network. The star signal-caller was diagnosed with a left-foot sprain after an X-ray, and he'll undergo more tests on Friday, according to Albert Breer of MMQB.
The veteran pivot went 4-of-6 passing for 30 yards, and he was sacked twice before leaving the game.
Newton didn't play in the Panthers' first two preseason games while continuing to recover from offseason surgery on his throwing shoulder.