Coach Doug Marrone said that Williams told trainers he had a sore foot.
"We decided we want to hold him out of practice, and let our medical staff evaluate him," Marrone said.
Williams was in uniform on Sunday evening, but watched from the sidelines during team drills. After signing a six-year, $100 million contract, Williams was limited for much of last season with a wrist injury.
"It's more of a disappointment for the individual," Marrone said. "Mario's put in a lot of hard work. We tend to forget how much work they put in, and we have a player who definitely wants to be out there."
Meanwhile, Pro Bowl defensive lineman Kyle Williams was also held out of team drills on Sunday evening, but participated in individual drills. Williams missed organized team activities this offseason while recovering from Achilles surgery.
"We're working him back in," Marrone said. "You'll see him progressing into the practices as we go."