How much does Manuel's loss hurt Bills?

This much is certain: EJ Manuel's latest injury is a blow to his development.

The Buffalo Bills had decided to ride their rookie quarterback this season, taking the bumps in the road as they came. It was the type of environment in which Manuel could work through his mistakes and build a foundation for an NFL career.

After all, that's the path general manager Doug Whaley and head coach Doug Marrone chose for Manuel. Even after Kevin Kolb's season was ended by a concussion, they could have brought in another experienced quarterback to compete with their first-round pick.

But they didn't, because they felt giving Manuel the experience -- an NFL baptism by fire -- was in Manuel's best long-term interest.

"My philosophy has always been, the greatest experience in the world is being in there playing," Marrone said Wednesday. "Some people don’t have that philosophy. Some people think sitting behind and seeing someone [is better]."

It was a decision that Marrone and Whaley, both in their first season on the job, could afford to make.

So naturally, Manuel suffering his second knee injury of the season diminishes the benefits he would have received from playing, no matter how much he can glean from watching the game from the coaches' booth, as he will do Sunday.

"I think I would be wrong to say that it hasn’t hurt him," Marrone said. "He missed some time with the first one. [He] got himself ready to come back, real short, which obviously everyone appreciates and [he's] again now missing some time here."

The Bills' focus now turns to preparing practice squad call-up Thad Lewis, who entered the NFL in 2010, to start Sunday against the Cincinnati Bengals.

That begs the question: If the Bills had to deal with the ups and downs of a rookie quarterback by starting Manuel, does turning to Lewis change anything?

Consider this: Lewis is on his fourth NFL team, but rarely has he hit the open market. After being waived by his original team, the St. Louis Rams, in Sept. 2011, he was claimed by the Cleveland Browns. After being waived by the Browns in May, he was claimed by the Detroit Lions.

And then, in late August, Lewis was traded to Buffalo. The Lions received one of the Bills' better special-teams players last season, linebacker Chris White, in return.

So it's clear that NFL teams have seen something in Lewis. At 6-foot-2, 200 pounds, he's slightly undersized for his position. But the Duke product has a reputation of being a smart, level-headed passer, much like Manuel.

For what it's worth, Lewis played well in the preseason.

When Lewis was called upon to start in Week 17 for the Browns last season, the results were also impressive: He went 22-for-32 passing (68.8 percent) for 204 yards, one touchdown and one interception.

The reality, still, is that Lewis would shock the NFL if he puts up big numbers Sunday against a Bengals defense that has held opposing quarterbacks to fewer than 300 yards passing in 19 consecutive games, the longest such streak in the NFL.

But that's not the point. What's more important is this: all things being equal, does Lewis actually give the Bills a better chance to win, right now?

Consider Manuel's performance to date:

On the season, Manuel has posted a 42.2 QBR, which ranks 23rd among qualifying quarterbacks. His 56.7 percent completion percentage slots him 26th in the NFL.

So is it fair to say that Manuel hasn't lit it up this season?

"Not lighting up, compared to maybe the rest of the NFL veteran quarterbacks, I wouldn’t disagree with you there," Marrone said Wednesday. "[But] I think if you go back and study all the first-year quarterbacks and where they were in those games, I think he’s pretty darn comparable when you look at it."

Regardless of how Manuel's play so far is evaluated, being ranked in the bottom quarter of the NFL in most of his passing stats leaves an opportunity for the Bills to improve at the position.

Whether Lewis, in just his second career start, has a chance to do that could determine whether there is truly a drop-off from Manuel to Lewis.

"I’m going to wait to hold off and see how Thad plays. If Thad goes out there and plays extremely well, I’ll be able to answer that question saying, ‘Hey, you know what? Yes, there’s not a big difference and Thad went out there and took advantage of this opportunity,'" Marrone said. "If he doesn’t I’d say, ‘Hey, you know what? It’s a difficult situation.’ I think a lot of it will be based on his performance in the game because in practice he looks good."