Re-setting Bills' quarterback depth chart

It was a busy Sunday for the Buffalo Bills. Hit with news that quarterback Kevin Kolb could be facing a career-ending concussion, Buffalo signed free-agent quarterback Matt Leinart and traded with the Detroit Lions for quarterback Thad Lewis.

With 13 days before the Bills open their regular season against the New England Patriots, their picture at quarterback is less clear than it has been at any point this preseason.

Here's a breakdown of what the Bills must sort through:

EJ Manuel -- The rookie's health remains Buffalo's biggest concern. The 16th overall pick underwent a minor procedure on his left knee last week, and the team said he is out for the remainder of the preseason. That leaves questions about if Manuel will be ready for the Patriots on Sept. 8. Even if he is not 100 percent, Manuel's return would stabilize the offense and calm a quarterback situation that has made national headlines in recent days.

Kevin Kolb -- ESPN NFL Insider Adam Schefter reports that Kolb has a "serious" concussion, one that could end his career. Kolb is still undergoing tests and his condition could improve, but the Bills want to be extra careful with Kolb, given his concussion history. Kolb could be a candidate to go on injured reserve with a designation to return, but it's also possible that the Bills shut him down for the season.

Matt Leinart -- The Bills worked out Leinart on Sunday and signed him afterward. The 30-year old has bounced around after his career with the Arizona Cardinals was largely a disappointment. The former 10th overall pick in the 2006 draft would be the most likely to start Week 1 if Manuel isn't ready to go. Having a lefty quarterback would be a slight adjustment for the Bills' offense, and Leinart will need to take a crash course in offensive coordinator Nathaniel Hackett's playbook, but his seven years of experience would be the best bet against the Patriots.

Jeff Tuel -- For the final three quarters of Saturday's preseason loss to the Washington Redskins, Tuel was the only healthy quarterback on the Bills' roster. Now, he returns to a backup role. It may actually be good news for Tuel, who was an undrafted rookie, needs time to develop. Starting the opener, although still possible, would be putting Tuel in a very difficult spot. He has performed well this preseason and should stick on the 53-man roster.

Thad Lewis -- Now in his fourth season out, Lewis is an athletic option at quarterback who was buried on the Lions' depth chart. He'll face his former team on Thursday in the Bills' preseason finale, but his future with Buffalo is murky after that. If Manuel is healthy, then Lewis will be in the same spot he was in Detroit: in danger of being cut. His best bet to stick is if Leinart struggles.