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.
Information from ESPN.com's Mike Rodak was used in this report.