Allen played almost the entire first half until he was removed from the game by an NFL concussion spotter with 16 seconds remaining in the second quarter. Allen, whose helmet hit the turf when he was hit by a Bengals defender after throwing the ball away, was later cleared to return but did not re-enter the game.
Allen, the No. 7 overall pick in the draft, completed 6 of 12 passes for 34 yards. In eight first-half possessions, Allen and the Bills' first-team offense gained four first downs, scored no points and ended the half with minus-5 net passing yards.
"I didn't do a good enough job getting the ball out on time and into the playmakers," he said. "Holding onto the ball is not going to be great most of the time."
The Bills had previously given Allen time with the third-team offense in the Bills' preseason opener and played him with the first-team offense for part of their second preseason game. Sunday marked his first time starting a game.
"Getting out there with the first team, obviously it's moving really fast," he said. "To see that speed, it was eye-opening. They have a really good defense. They came out and they brought it. But at the same time, we had plays in place that could've worked if I got the ball out in time. It just didn't happen enough tonight.
"Sometimes when the play clock got a little low and I couldn't really dissect what they were doing and understanding what they were doing, it's tough on a quarterback."
Allen has completed 24 of 44 passes for 210 yards and two touchdowns this preseason.
Nathan Peterman replaced Allen for the final three plays of the first half and played the entire second half, completing 16 of 21 passes for 200 yards, including a 17-yard touchdown to tight end Jason Croom. Peterman has completed 33 of 41 passes this preseason for 431 yards, three touchdowns and one interception.
Bills coach Sean McDermott said after Sunday's 26-13 loss to the Bengals that he would need to watch the tape of the game before deciding when he will name a starting quarterback for the regular-season opener against the Baltimore Ravens.
AJ McCarron, who started and suffered a shoulder injury in the Bills' second preseason game, was in uniform Sunday but did not play. McDermott said McCarron was the third quarterback for the game and would have been able to play.
McDermott did not know which quarterback would start Thursday's preseason finale against the Chicago Bears.