CLEVELAND (AP) — Buffalo quarterback AJ McCarron sustained a potentially serious shoulder injury, throwing the Bills’ quarterback situation into total disarray, during a 19-17 win over the Cleveland Browns on Friday night.

McCarron, who signed with Buffalo as a free agent for a chance to start after four years as a backup in Cincinnati, completed just 3 of 6 for 12 yards during four series.

The 27-year-old didn’t show any obvious signs of being hurt — he was hit hard from behind by Myles Garrett and sacked by Larry Ogunjobi — and the Bills didn’t disclose his injury until the fourth quarter.

McCarron is competing with Nathan Peterman and rookie Josh Allen for Buffalo’s starting job.

Allen, the No. 7 overall pick, out-performed McCarron and Peterman rallied the Bills (2-0) with a late touchdown pass to tight end Nick O’Leary.

Rookie Nick Chubb and Carlos Hyde had touchdown runs for the Browns (1-1).

The Bills have wanted to take a slow approach with Allen, letting him watch and learn behind McCarron and Peterman. However, those plans may have to be scrapped.

Peterman who started two games as a rookie in 2017, was 8 of 10 for 113 yards and a score.

Allen fired a 2-yard TD pass to Rod Streater in the second quarter and led the Bills on three scoring drives. He completed 9 of 13 passes for 60 yards and was sacked once.

Not only did he outshine McCarron, but he stole some of the spotlight from Baker Mayfield, the No. 1 overall pick making his home debut. Mayfield finished 7 of 13 for 75 yards.

Cleveland starting QB Tyrod Taylor didn’t do much against his former team, completing 4 of 7 pass for 22 yards in four series. The Bills traded him in March to the Browns.