Without going into detail, general manager Doug Whaley announced Tuesday the team released Kolb after he failed a physical.
The move came shortly after the start of the NFL's free agency period and a few days before Kolb was due a bonus as part of the two-year contract he signed with Buffalo in April. Now there are questions whether Kolb's career might be over after he sustained what was at least his third concussion in seven seasons.
The latest occurred during the first quarter of a 30-7 preseason loss at Washington on Aug. 24, when Kolb was kneed in the back of the head at the end of a scramble. Diagnosed with concussion-like symptoms, Kolb was placed on injured reserve a week later and spent much of the season recovering at his home in Texas.
The Bills were Kolb's third team since being selected in the second round of the 2007 draft by Philadelphia. A concussion in 2009 resulted in Kolb losing the starting job to Michael Vick in Philadelphia. He then spent two seasons in Arizona, where he failed to secure the starting job because of an assortment of injuries.
Buffalo signed Kolb to provide veteran experience and leadership behind rookie starter EJ Manuel.
The Bills made two moves in free agency by re-signing veteran kicker Dan Carpenter, who signed a four-year contract, and tight end Mike Caussin.
Carpenter returns to Buffalo after what proved to be a successful one-year tryout as an injury replacement after rookie sixth-round draft pick Dustin Hopkins hurt his groin six days before the season opener.
The sixth-year player proceeded to enjoy a career year. Carpenter's 33 field goals were a career high and tied the Bills' single-season record set by Steve Christie in 1998.
Carpenter's return leaves Hopkins' future uncertain.
Carpenter was so eager to re-sign with the Bills that he, his wife Kaela and son Colby arrived at the team's headquarters to complete negotiations after traveling from his home in Florida on Tuesday. Under NFL rules, Carpenter was not allowed to re-sign with Buffalo before free agency began because he had signed a one-year deal at the league veteran minimum.
''I don't think we would have got on the plane if we didn't think there was a future here in Buffalo,'' Carpenter said. ''For us, it was a no-brainer to come back to Buffalo. We were comfortable and loved it here last year.''
The signing ends what was a tumultuous stretch for Carpenter, who took a circuitous route to Buffalo after spending his first five seasons with the Miami Dolphins.
Carpenter's contract was terminated by the Dolphins in mid-August, and he failed to land a job in two brief stints with Arizona and the New York Jets. Carpenter was on his way for a tryout with Cleveland before making a detour to Buffalo.
''To be able to go back somewhere and be wanted is where you would like to go,'' he said. ''You're very fortunate in this league for that to happen.''
A 2009 Pro Bowl selection, Carpenter provided Buffalo a veteran and dependable presence.
He hit 33 of 36 field-goal attempts, including 29 of 30 from inside 50 yards last season. With a 91.67 percent success rate, Carpenter fell just short of breaking Rian Lindell's single-season record of 92 percent (23 of 25) set in 2006. And Carpenter's 131 points ranked third on the Bills single-season list.
Overall, his 160 field goals since 2008 rank fourth among kickers during that span.
Caussin returns after he was eligible to become a restricted free agent, and despite missing the past two seasons because of injuries. He was sidelined last season with a hip injury sustained early in training camp, and missed 2012 because of a knee injury.
Caussin had five catches for 41 yards in six games, including two starts, with Buffalo in 2011 after being promoted off the team's practice squad. He broke into the NFL with Jacksonville in 2010 as an undrafted free agent, but did not play a game with the Jaguars.
The Bills have a need at tight end, with starter Scott Chandler becoming a free agent.
AP NFL website: www.pro32.ap.org