Charles Clay has had chronic knee trouble since joining the Buffalo Bills as a highly paid restricted free agent in 2015.

The problem has persisted during the team's current offseason workouts, and it is something that coach Sean McDermott is worried about.

"We are concerned with Charles' knee situation," McDermott told reporters Thursday before the Bills took the field for an OTA workout. "It's something we have to manage moving forward in order to have him on the field for us, which is important moving forward. He's a weapon for us."

McDermott did say that Clay has taken part in drills, but the team is being cautious about how much work he receives.

"He's participated in most all of it," the coach said. "That said, just like with all of our players, we have to put them in position to be successful, Charles no different. So if managing his reps, if that's what we have to do, then we'll continue to do that."

McDermott added that Wednesday's signing of free-agent tight end Wes Saxton was not related to Clay's knee issue. Besides Clay and Saxton, the Bills have five other tight ends: Nick O'Leary, Blake Annen, and rookie free agents Jason Croom and Keith Towbridge.