Under heavy duress behind the Bills' starting offensive line against the Browns in Friday's second preseason game, AJ McCarron sustained a hairline fracture to his right collarbone, the Buffalo News' Vic Carucci first reported.

McCarron, whom the Bills signed to a two-year, $10 million contract this offseason as a potential veteran place holder before trading up in Round 1 to select Josh Allen seventh overall, was making his first start, one week after Nate Peterman got the call in Buffalo's three-man QB competition.

Well, now it appears to be a two-man battle, at least for a while, as McCarron's injury is expected to sideline him several weeks. And whittled down to Allen vs. Peterman, the rooke, who played well Friday night, might be the favorite to land the job.

Allen, easily the most physically impressive and mobile of Buffalo's three passers, probably stands the best chance to survive behind what might be the worst offensive line in football, a unit that lost its three best performers in the offseason — LT Cordy Glenn in the trade to Cincinnati that added ammo for the Allen deal and C Eric Wood and LG Richie Incognito to retirement.

We saw Allen's speed and nifty pocket movement Friday, when he evaded the pass rush on his first touchdown and also picked up first downs twice with his legs while leading the offense to points on all three of his drives. He clearly has elusiveness and an extra gear that McCarron and Peterman lack. But does Allen's lack of experience mean he'll need those unique attributes more than the veterans because he's not as equipped to read NFL defenses and avoid trouble?

The Bills also have very little in the way of passing-game weapons, with Kelvin Benjamin and his chronic knees and underachieving Corey Coleman not exactly the type of reliable targets a rookie passer should be asked to lean on, particularly behind a line full of replacement-level blockers.

Allen, of couse, is the franchise's biggest, most important investment, and mobile or not, putting him behind that line would be nothing if not risky. Remember, Allen is a raw prospect who was expected to require plenty of NFL seasoning before he was ready. Throwing him to the wolves, i.e., future Hall of Famer Terrell Suggs' Ravens in Week 1 and potential future Defensive Player of the Year Joey Bosa's Chargers in Week 2, would be nothing if not risky.

Indeed, this qualifies very much as a damned if they do, damned if they don't proposition for the Bills. Peterman, you'll remember, tossed five interceptions against the Chargers — before halftime — in his NFL debut a year ago, when the then-fifth-round rookie clearly wasn't ready, before Buffalo quickly turned back to Tyrod Taylor, whom it had just benched.

Peterman, although not nearly as talented Allen, hailed from a pro style offense and had more experience starting against high level college competition. He's also looked sharp this preseason, completing 17-of-20 for 231 yards, two touchdowns and an interception (Allen has completed 18-of-32 for 153 yards and two touchdowns without a pick).

But Allen clearly is the future, and for better or worse, it might be starting sooner than expected in Buffalo.