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.
Hobbled by injuries most of the year, Clay finished strong, catching 21 passes for 229 yards and three touchdowns in his final four games. He was the #12 TE in the second half of the season and averaged the 9th-most targets in that span. His ADP is unlikely to rise given this report.