http://espn.go.com/nfl/trainingcamp13/story/_/id/9600221/concussion-kevin-kolb-buffalo-bills-threatens-career-source-says

Buffalo Bills quarterback Kevin Kolb suffered a concussion in Saturday's preseason loss to the Washington Redskins, a league source told ESPN NFL Insider Adam Schefter.

Per the source, the Bills are proceeding as if the concussion, which was termed "serious," could be career-ending.

Kolb will undergo a battery of tests and the Bills do not want to rush him back even if he can continue his career, the source told Schefter.

While diving for a first down in Saturday's game, Kolb was kneed in the helmet by a Redskins defender. He remained on the field for the final four plays of the drive before departing for the locker room with what the team called concussion-like symptoms.

Kolb, who turned 29 on Saturday, missed time in 2010 and 2012 with concussions, a history that has the Bills concerned.

The Bills are already without rookie EJ Manuel, who underwent a minor procedure on his left knee last week.

On Sunday, the Bills signed veteran quarterback Matt Leinart and traded with the Detroit Lions for backup quarterback Thad Lewis.