ORCHARD PARK, N.Y. -- Rookie running back Karlos Williams returned to Buffalo Bills practice Friday, nearly three weeks after undergoing an undisclosed medical procedure.

Williams, a fifth-round pick from Florida State who could see an expanded role after the Bills released veteran running back Fred Jackson, expects to play in the Bills' opener Sept. 13 against the Indianapolis Colts.

"Most definitely, most definitely," he said. "Definitely on special teams, try to work myself into the rotation as the week goes on. Try to get in there for the first game next week."

He did not specify the ailment that led to his hospitalization Aug. 17 and his subsequent surgery.

"Bad things happen to people sometimes, you can say that," Williams said. "But no, it was kind of a freak accident that kind of happened. A lot of pain. The trainers definitely took care of that. They found out what it was, got it taken care of and had a quick surgery. And actually a pretty quick recovery. I'm just happy to be back from that. But it was a very, very delicate situation."

Coach Rex Ryan has previously referred to Williams' injury as being to a "sensitive" area.