Bills Kolb FootballThe Buffalo Bills’ quarterback battle between Kevin Kolb and E.J. Manuel has taken an unforeseen plot twist.

During Saturday morning’s practice session, Kolb, running between fields, slipped on a wet rubber mat, “stumbled awkwardly” and injured his knee, according to The Associated Press.

Bills coach Doug Marrone said the injury was not serious and that he expects Kolb to return to practice within a few days.

After stumbling, Kolb had trouble standing and had to receive support from Bills trainer Bud Carpenter, according to the report. He then apparently got angry and “tossed down his helmet in frustration.”

Kolb is trying to grab control of the Bills’ starting quarterback job heading into his seventh season in the league. He spent his last two seasons with Arizona, where he signed a five-year, $64 million contract in 2011 that he never came close to living up to. He started just 14 games between the two seasons, finishing his injury-ridden stint with 17 touchdowns and 11 interceptions. He was cut this offseason and joined Buffalo, signing a two-year, $13 million deal.

Manuel, who was drafted in the first round this year out of Florida State, figures to give Kolb a serious run for his money, however. And episodes like Saturday morning’s slip-up aren’t doing him any favors.