Allen's arm was hit while he was following through on a throw, and Nathan Peterman entered the contest in his place.
According to Mike Rodak of ESPN, the rookie didn't talk to reporters after the loss and was "noticeably favoring his arm while changing. Did not move injured right arm as much as he could."
Considering the Bills drafted Allen with the No. 7 overall pick, they tabbed him as the future franchise quarterback. Losing him for significant time would cut into his development opportunities while also forcing them to turn elsewhere under center until he is back.
The 22-year-old has 832 passing yards, two touchdown throws and five interceptions in his first season in the NFL ranks.
While at Wyoming, Allen threw for 3,203 yards and 28 touchdowns in 2016 and followed up with 1,812 passing yards and 16 touchdowns through the air in 2017. Interceptions were a concern in the college ranks as well considering he threw 21 picks in his final two years.
Look for Buffalo to hand the quarterback reins to Peterman if Allen is sidelined.
Peterman earned the starting job in Week 1, but Buffalo quickly turned to Allen for the following game. The Pittsburgh product famously threw five interceptions in a game last season and has struggled to establish himself as an effective quarterback at the NFL level. He threw a disastrous pick-six in the final minutes of Sunday's loss.