Allen (concussion) was listed as a limited participant in Thursday's practice, Chris Brown of the Bills' official site reports.
The participation level represents no change to Allen's listing from Wednesday, indicating that he hasn't advanced to the fifth and final stage of the concussion protocol. According to Marcel Louis-Jacques of ESPN.com, Allen was mostly limited to throwing drills during Thursday's session, and coach Sean McDermott was unwilling to shed much light on the quarterback's potential to play Sunday in Tennessee. In the event Allen doesn't gain clearance to suit up, Matt Barkley would step in to start for the Bills, while Davis Webb would likely be promoted from the practice squad to serve as the team's second-string quarterback.