Lewis was held out of practice for the third straight day Friday due to sore ribs, and his exact status for Sunday still hasn't been revealed.
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"I spoke to Thad, I spoke to the trainers," he said. "I know there was a report out there from a league source. I'm hoping the league source is right. Because I really don't know right now. It's 50-50. Trust me."
In the case that Lewis can't play, the Bills will choose between undrafted rookie Jeff Tuel and veteran Matt Flynn to get the start. Tuel has been with the team the longest to this point, and probably has the strongest case to start between the two options. Marrone said they're doing their due diligence though.
"There are some things that are going on. I'm gonna keep that private just for schematics of what's going on," he remarked. "Both players are taking reps though, and both of them are doing a nice job."
Both Lewis and Teul are serving as backup to first round draft pick EJ Manuel.
With rookie starter Manuel (sprained right knee) still not cleared to play, and veteran backup Kevin Kolb (concussion) out for the season, the Bills could be down to their fourth-string quarterback after Lewis was hurt in a 35-17 loss at New Orleans last weekend.
Making his third consecutive start since being promoted off the practice squad, Lewis was initially injured on the first play from scrimmage during last week's game, when New Orlans linebacker David Hawthorne struck the quarterback with a helmet-first hit into his right ribs. Lewis fumbled the ball and had difficulty getting off the field before returning for the next series and completing the game.
Lewis has gone 1-2 as a starter since Manuel was hurt in a 37-24 loss at Cleveland on Oct. 3. Lewis has put up respectable numbers in Buffalo, in completing 62 of 103 passes for 652 yards, with three touchdowns and two interceptions.
Manuel practiced for the first time on Wednesday, but has already been ruled out from playing.