ORCHARD PARK, N.Y. -- Buffalo Bills wide receiver Sammy Watkins was among a small group of notable players not spotted at voluntary offseason workouts, which began Monday.

It's unclear if Watkins was behind the scenes rehabbing an injury, or whether he was not in the facility. Coach Rex Ryan will address reporters at 1 p.m. Monday.

In addition to Watkins, right tackle Seantrel Henderson and defensive tackle Kyle Williams were not spotted on the field Monday. Henderson ended last season on the non-football illness list, while Williams ended last season on injured reserve after undergoing knee surgery.

Safety Aaron Williams, who ended last season on injured reserve with a neck injury, took part in the start of the workout Monday. Wide receiver Marcus Easley was also participating in stretching with his teammates after suffering a dislocated kneecap and breaking his knee in three places during a game last December.

Defensive lineman Corbin Bryant was participating in workouts. The Bills announced Monday that Bryant, a potential starter, had signed his restricted free-agent tender.

Wide receiver Marquise Goodwin, who is attempting to qualify for the 2016 Summer Olympics in track and field, was also present, along with both quarterbacks under contract: Tyrod Taylor and EJ Manuel.