ORCHARD PARK, N.Y. -- When Buffalo Bills left guard Chris Williams returned from a back injury to practice fully last week, the assumption was that he would be ready to play in Saturday's preseason loss to the Tampa Bay Buccaneers.

That turned out not to be the case, as Williams sat out that game and has not practiced since. While Bills coach Doug Marrone didn't say whether Williams has suffered a setback in his recovery, he didn't offer any timetable for his return.

"I don't know. I really don't. Am I concerned? Yes. I'm not going to sit here and say I'm not concerned," Marrone said.

However, Marrone said that he was a "little excited" about the opportunity to play fifth-round pick Cyril Richardson, who started Saturday's game in Williams' place.

"There's some things that he showed that I have no doubt, having coached that position before, to say that he's a future starter," Marrone said.

Marrone stopped short of saying that there is a competition between the rookie and Williams, who signed a four-year, $13.5 million contract on the offseason.

"I wouldn't say, not right now. Once Chris is healthy, Chris is better," Marrone said.