Carolina quarterback Cam Newton left the Panthers' Thursday night preseason game against the host New England Patriots late in the first quarter due to a left-foot injury.
The team referred to it as a foot injury, with multiple outlets reporting it is a foot sprain. ESPN reported the diagnosis was an ankle sprain.
Newton was hurt when he was sacked after scrambling in the pocket during his third series of the game. He limped off the field and trainers looked at his foot on the sideline before taking him back to the locker room.
The team announced shortly afterwards he would not return and he left the stadium after the game in a walking boot.
Panthers general manager Marty Hurney told the team radio network after the game, "We're hoping it's not too bad. ... We'll find out more tomorrow. But I hope it's not too bad."
Newton was making his preseason debut, his game first action since having shoulder surgery in the offseason. He went 4 of 6 for 30 yards, taking two sacks, before departing. Backup Kyle Allen replaced Newton.
Newton, 30, is entering his ninth NFL season. Last season, he completed 67.9 per cent of his passes for 3,395 yards, 24 touchdowns and 13 interceptions in 14 games, missing the final two due to the shoulder injury.
The Panthers open the regular season September 8 against the visiting Los Angeles Rams.