Buffalo Bills quarterback Kevin Kolb entered the preseason vying for the team’s starting spot with rookie EJ Manuel. He was initially hampered by a knee ailment, and he’s now recovering from a concussion. While the head injury is lessening his chances of entering the regular season as the Bills’ starter, there is also concern that it could be career-ending, according to Tim Graham of the Buffalo News.

Following Kolb’s concussion, the Bills signed former first-round pick Matt Leinart and traded for quarterback Thaddeus Lewis. These weren’t good signs for Kolb’s diagnosis, and it turns out they were the result of grave concern surrounding the 29-year-old.

It’s still early in the recovery process, and it’s hard to tell if the head injury will develop into something that will cause Kolb to consider retirement. Still, Kolb did suffer two concussions that he considered to be “major” earlier in his career. He was then hampered for roughly a month after sustaining another concussion late into the 2011 season.