Coach Sean McDermott announced the decision Monday. He said after the Bills' 41-10 win Sunday over the New York Jets that he would need time to decide on a starting quarterback for when the Bills return from their upcoming bye week.
"Josh is our starter, when healthy, and his development is important for him and for us moving forward," McDermott said Monday. "Getting experience -- you've seen a lot of quarterbacks this season play -- and it's important that he gets as many reps as he can get in live game action."
Allen has not played since spraining his right elbow during an Oct. 14 loss to the Houston Texans. A source told ESPN's Adam Schefter before Sunday's win that Allen had been pushing to play and felt ready to go against the Jets before the team opted to hold him out. The source added that Allen, who returned to practice last week, was expected to be ready to return after the bye week.
In six games this season, including five starts, Allen has completed 54 percent of his passes for two touchdowns and five interceptions.
McDermott's choice to start Allen comes after Matt Barkley started Sunday in place of both Allen and veteran quarterback Derek Anderson, who remained in the concussion protocol Monday. Barkley, whom the Bills signed Oct. 31, completed 15 of 25 passes for 232 yards and two touchdowns.
"I thought Matt performed extremely well," McDermott said Monday. "There's certainly some plays he'd like to have back, but to come in and do what he did on a short run-up, basically, was very impressive."
Barkley's 90.2 Total QBR was the Bills' sixth-highest in the past 10 seasons. Buffalo gained 312 total yards and scored four offensive touchdowns in the first half, which were both their best marks in a first half since the 2000 season finale.
The Bills have four quarterbacks on their 53-man roster, all of whom have started games this season. McDermott said he and general manager Brandon Beane will discuss this week whether they will keep all of their quarterbacks on the roster.
Buffalo's odd quarterback out could be Nathan Peterman, who has thrown one touchdown and seven interceptions on 81 pass attempts this season. The Bills opted to start Barkley on Sunday despite his limited knowledge of the playbook over the interception-prone Peterman.
"I'm still confident in Nate," McDermott said Monday.