Bills coach Doug Marrone provided few details regarding the nature of Williams' injury. Marrone wouldn't say which foot Williams had hurt or how and when it happened.
"Mario reported to our athletic training staff that he had a sore foot," Marrone said after the two-hour-plus session at the Bills' training-camp facility in suburban Rochester. "So what we wanted to do was hold him out of practice and let our medical staff evaluate him."
Marrone couldn't say how much time Williams might miss because the injury still is being evaluated. The Bills are back on the field Monday afternoon.
Williams declined comment after practice, and he deferred all questions to Marrone.
After acknowledging he was disappointed to miss the opening session, Williams then apologized that he couldn't say anything more.
Williams did not appear to be walking with a limp. He did not participate in any individual or team drills Sunday, and he spent much of practice watching from the sideline with his helmet on. On several occasions, he was spotted bending over frontward to stretch out his back.
The foot injury came as a surprise after Williams did not indicate he was experiencing any health issues upon reporting to camp Friday.
Williams was motivated upon arriving at camp, saying he wanted to put behind his inconsistent first season in Buffalo, which came after he signed a six-year, $100 million contract with the team in free agency. Williams led the Bills with 10.5 sacks, but his performance was hampered in the first half of the season because of a left wrist injury that was surgically repaired in late October.
Copyright 2013 by The Associated Press