The Bills are already thin at linebacker, making the position a priority in free agency and the draft in the coming months.
Wilson was a respected leader and voted a five-time team captain during his eight seasons in Buffalo. He was also the team's NFL Players Association representative.
Wilson was highly regarded for his work ethic and resilience. He broke in with the Bills as a receiver in 2005 before being converted into a safety while spending the 2006 season on the team's practice squad. He made an immediate impact at his new spot in 2007, when Wilson started nine games and had two interceptions, both of which he returned for touchdowns.
Last season, Wilson finished second on the team with 98 tackles but no interceptions. Most notably, he had two potential fourth-quarter interceptions drop from his hands in losses to Tennessee and St. Louis — both decided in the final minutes.
Wilson was also entering the final year of his contract, and due to make a $2.9 million base salary.
Second-year player Da'Norris Searcy began challenging Wilson for the starting job last season.
The Bills have a big question mark at free safety, with starter Jairus Byrd eligible to become an unrestricted free agent next month.
Veteran defensive lineman Spencer Johnson, defensive end Kyle Moore and linebackers Bryan Scott, Kirk Morrison and Shawne Merriman have also completed the final years of their contracts.
Buffalo's defense is prepared to undergo yet another transformation under Pettine, the unit's third coordinator in three years. Pettine is more accustomed to running a 3-4 alignment after the Bills reverted to a 4-3 system under former coordinator Dave Wannstedt last year.
The Bills struggled in making the transition last year, and despite the free-agent addition of defensive end Mario Williams, who was signed to a six-year, $100 million contract.
Buffalo (6-10) finished 31st in the NFL against the run, and 26th in allowing an average 27 points per game.