Robert Griffin III has already suffered a setback in his comeback season.
The Cleveland Browns quarterback, who joined as a free agent in March, sustained a left shoulder injury in Sunday's 29-10 season-opening loss to the Eagles and has been placed on injured reserve.
Tests revealed a fractured coracoid bone in Griffin's shoulder, but the team said surgery is not required "at this time".
Veteran Josh McCown is slated to be his replacement in Cleveland's week-two home opener against the rival Baltimore Ravens.
"It's very unfortunate, Robert came in and has worked extremely hard to learn our offense and earn the respect of his team-mates," Browns coach Hue Jackson said in a statement.
"This is a tough loss because everyone has seen how invested he has been in this team and his dedication to the work needed to improve his craft. We all know these are the realities of the NFL, injuries occur and you have to find ways to overcome them so they don't impede your progress.
"Robert will do everything in his power to rehab and get healthy but Josh McCown is on this roster for a reason and we have great confidence in him. He is more than capable.
"His veteran presence has been an asset to our team throughout our process of preparing for the season. We look forward to him assuming the role of the starter and leading our offensive unit."
Griffin's season is not necessarily over, as he could be designated to return from injured reserve after missing at least eight games. The Browns will re-evaluate him in three to four weeks.