Bush, 23, was set to make $10.9 million in the option year. Instead, he'll hit free agency after the 2022 season.
The Steelers traded up to select Bush No. 10 overall in the 2019 NFL draft in hopes he could fill Ryan Shazier's role.
Bush, a Michigan product, tore his ACL five games into the 2020 season and wasn't the same after. After posting 109 tackles his rookie season, Bush had just 70 in 2021, along with two sacks, one forced fumble and one fumble recovery. In his rookie season, Bush had four fumble recoveries, including one he returned for a touchdown.
The Steelers signed inside linebacker Myles Jack in free agency, but the rest of the position group is a work in progress with second-year linebacker Buddy Johnson, Robert Spillane, Ulysees Gilbert III and Marcus Allen rounding out the depth chart.