QB AJ McCarron went down with a shoulder injury during the Buffalo Bills’ preseason game against the Cleveland Browns on Friday. While the team has not confirmed the severity of the injury yet, the Buffalo News is reporting the he suffered a broken collarbone.

McCarron was competing with rookie QB Josh Allen and second-year QB Nathan Peterman for the starting quarterback job, getting the nod for the first time on Friday after coming off the bench last week against the Carolina Panthers.

The former fifth-round pick had limited regular season experience during his first four years in the NFL, starting three games for the Cincinnati Bengals back in 2015. Not including the playoffs, McCarron was the 16th-highest graded quarterback that season with a 71.4.

Over that span, he led the NFL with an 81.1 adjusted completion percentage. His passer rating from a clean pocket that season was 117.1, the second-best mark in the league behind only Russell Wilson.

With McCarron sidelined, the Bills are now forced to rely on one of their young quarterbacks to step up into the starting role.

Through two preseason games, Peterman holds the second-highest adjusted completion percentage of any quarterback at 90.0, but so far he’s the lowest-graded of the Buffalo quarterbacks at 64.9.

Allen leads the league in rushing grade among quarterbacks this preseason at 79.4, averaging 4.0 yards after contact per carry.

The rookie has used his legs to extend passing plays as well, holding a 113.8 passer rating on plays that last 2.5 seconds or more, the 10th-best mark among signal-callers this preseason.

The two inexperienced quarterbacks have two more preseason games to show the Bills which one deserves to start Week 1.