ORCHARD PARK, N.Y. (AP) — Buffalo Bills quarterback AJ McCarron is getting a second opinion to determine the severity of an injury to his throwing shoulder, and veteran defensive tackle Kyle Williams is in jeopardy of missing the start of the regular season with a knee injury.

Coach Sean McDermott declined to provide much more detail on Sunday, shortly before the Bills returned to practice two days after both players were hurt in the first half of a 19-17 preseason victory at Cleveland.

McDermott said he could not provide an update on McCarron because tests on his right shoulder were not "totally conclusive." As for Williams, the coach listed the starter as being week to week.

While the Bills practiced outdoors, Williams was spotted by The Associated Press walking into the weight room. He walked without a noticeable limp but had a long black wrap covering most of his right leg.

Williams was injured when a Browns player rolled up on the back of his right leg during Carlos Hyde's 19-yard run up the middle on the third play of the second quarter. Williams had difficulty putting much weight on the leg while being helped off the field and was spotted wearing a large brace afterward.

McCarron was hurt during one of Buffalo's first four series against Cleveland, during which he was sacked once and hit several other times.

McCarron's injury opens the door for rookie first-round draft pick, John Allen, or returning backup, Nathan Peterman, to land the starting job in what's been an offseason-long competition.

With the Bills being cautious in electing not to rush Allen's development , McCarron was considered the initial front-runner for the job to open the season. He is the most experienced quarterback on the roster after spending his first four NFL seasons as Andy Dalton's backup in Cincinnati before signing with the Bills in free agency in March.

McCarron struggled in his first preseason start and had little help from an offensive line that had difficulty stopping the Browns' pass rush.

He was sacked once, hit several times and finished going 3 of 6 for 12 yards during four series in which the Bills failed to generate a first down.

Allen replaced McCarron and led Buffalo on scoring drives — a touchdown and two field goals — on each of his three possessions. He finished 9 of 13 for 60 yards and showed poise by avoiding the pass rush and stepping up in the pocket to hit Rod Streater for a 2-yard touchdown pass in a third-and-goal situation.

He particularly cleaned up his inconsistencies as a passer after going 9 of 19 for 116 yards and a touchdown in overseeing the third-stringers during the entire second half of Buffalo's preseason-opening 28-23 loss to Carolina a week earlier.

Allen practiced almost exclusively with the third-string offense through spring and the first two weeks of training camp, before being elevated to second-string duties last week.

Peterman has put up the best numbers of the three. He's completed 17 of 20 attempts for 232 yards, with two touchdowns and interception.

He was selected in the fifth-round out of Pittsburgh last year and had a forgettable rookie season. McDermott's calculated gamble to bench Tyrod Taylor and start Peterman backfired after the rookie threw five interceptions in the first half of a 54-24 loss at the Los Angeles Chargers on Nov. 19.

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