Multiple reporters on scene indicate that while Kolb was moving between practice fields during the individual portion of practice, he slipped on a rubber mat and hurt the knee. Trainers examined the knee on the field, according to WGR 550's Sal Capaccio, and Kolb then removed his pads and headed into the locker room with help from head athletic trainer Bud Carpenter.
After practice, Bills head coach Doug Marrone called Kolb "day to day" and said that the quarterback had simply bumped his knee. He also told Mark Gaughan of The Buffalo News (via Capaccio) that the injury is not serious.
As he ran, Kolb slipped on a wet rubber mat and stumbled awkwardly at the Bills training camp facility in suburban Rochester on Saturday. Though he did not fall, he had trouble standing and put his arm around the shoulder of head trainer Bud Carpenter. Kolb then tossed down his helmet in frustration, before sitting down on the field.
Aside from Marrone's update, there isn't a clear indication yet on how serious the injury might be. It's unfortunate news for the oft-injured Kolb, as he's currently in a battle for the team's starting quarterback job with rookie EJ Manuel - and by all accounts, Manuel has an early lead in that race. Even if Kolb only misses today's practice, he's potentially losing ground in that battle; naturally, if he's out for longer, that battle looks much different.