The Jaguars released Jack on Wednesday, a day after the team came to terms with six players on the first day of the NFL's free-agency negotiating window.
One of those players was Foye Oluokun, who led the NFL in tackles last season with 192.
Jack, who will turn 27 in September, was the Jaguars' leading tackler last season with 108 and has had at least 107 tackles in three of the past four seasons.
He signed a four-year, $57 million extension that included $33.06 million guaranteed in September 2019, a deal that at the time made him the NFL's third-highest-paid inside linebacker. The Jaguars drafted him 36th overall after trading up two spots in 2016.
There were concerns about Jack's right knee before the draft, and he acknowledged to the New York Post in a pre-draft story that there may be some degenerative issues "but it's nothing extreme."
Jack has missed only nine games in his six-year career and has 513 tackles, 6.5 sacks, 3 interceptions and 4 fumble recoveries.
ESPN's Michael DiRocco contributed to this report.