They're dropping like flies in western New York.

A day after wide receiver Stevie Johnson pulled his hamstring while participating in a Buffalo Bills training camp drill, quarterback Kevin Kolb injured his knee in not-so-typical fashion.

Walking between fields Saturday morning, Kolb slipped on a rubber mat, forcing him to sit out the day's workout.

At the time of the incident, the Buffalo News reported Kolb didn't fall, but the awkwardness of the slip may have caused a pulled muscle.

Team trainers took a look at the 28-year-old's left knee and, according to the Bills' official Twitter feed, determined Kolb had "bumped his knee." He is listed day-to-day on the team's injury list.

Kolb, signed by Buffalo in March as a free agent, has a 78.9 career quarterback rating in 21 starts split between the Philadelphia Eagles and Arizona Cardinals.