ORCHARD PARK, N.Y. -- With rookie EJ Manuel sidelined for several weeks because of a right knee injury, the Buffalo Bills will start Thad Lewis at quarterback Sunday against the Cincinnati Bengals, coach Doug Marrone announced Monday.

Lewis, who spent the first five weeks of the season on the practice squad, was signed to the active roster.

"He can run, he can extend plays, he can run the read option. He can throw the ball extremely well," Marrone said. "One of the questions people are going to ask is, 'Does he know the whole system?' He does. He knows everything. He's as bright as hell."

Lewis said he has a "great grasp" of the Bills' game plan.

"Every week, you don't just sit there on the practice squad and not prepare as if you're the starter. That's your job. This is what you're supposed to do," he said. "You have to learn, you have to know the things that you need to do, so I've been doing that every week. It will be a regular week for me, except that I get the chance to start this Sunday."

The Bills are turning to Thad Lewis at QB with EJ Manuel sidelined. AP Photo/Bill Wippert

The Bills chose not to start undrafted rookie Jeff Tuel, who was the only healthy quarterback remaining on the roster. Tuel replaced Manuel in Thursday night's loss to the Cleveland Browns and went 8-of-20 passing for 80 yards and an interception that was returned for a touchdown.

"I don't doubt when people look at it and say, 'Wait a minute now, [Tuel] was here, behind your starter, and [Lewis] was on the practice squad. That doesn't make sense. Why wouldn't you go with the other guy and bring him up?'" Marrone said. "Jeff, in my opinion, is going to be a very good player. But what happened was we couldn't gain a third roster spot for the quarterback to bring Thad up [earlier]."

Marrone called Tuel a developmental prospect whom the team did not want to expose to waivers at the end of the preseason. He referred to Lewis, who has one career start but has been in the NFL since 2010, as a veteran.

Lewis, 25, was acquired in a trade with the Detroit Lions on Aug. 25 after Manuel underwent surgery on his left knee. A former undrafted free agent out of Duke, Lewis started last season's finale for the Browns.

"I think that the skill set with Thad, with the ability to run and extend, gives us a better chance," Marrone said.

Lewis said he was "confident" and doesn't have anxiety about making the start Sunday.

"It's football, something I've been doing since I was 5 years old," he said. "A lot of people don't understand, it's not my ability why I was on the practice squad, it's just certain situations. As long as you're confident in your ability, you can go out there and do the things that you need to do."

Marrone said the Bills will re-evaluate their quarterback situation on a weekly basis until Manuel returns.

"I think it's something that you have to look at from week to week," he said. "A lot of times the situation is going to dictate what you do next."

Buffalo worked out free-agent quarterbacks Pat White and Dennis Dixon on Sunday, but did not sign either. Marrone also acknowledged that the team had contact with Josh Freeman, who agreed to a contract with the Minnesota Vikings on Sunday night.

ESPN NFL Insider Adam Schefter contributed to this report.