The Texans acquired Johnson from the Cleveland Browns during training camp in 2019 for a third-round pick.
In 11 games for the Texans last season, Johnson rushed for 235 yards and a touchdown on 77 carries. The pass-catching running back had a career-low 28 receptions for 249 yards and a touchdown.
Johnson backed up Carlos Hyde in 2019 and David Johnson in 2020. During the 2020 season, he started in place of David Johnson when the starter missed time due to a concussion and spending a week on the COVID-19 list.
Martin was a second-round draft pick in 2016 and signed a three-year $33 million contract in 2019 that included more than $18 million guaranteed.
He was owed a $7.25 million base salary in 2021 and will have a dead money charge of $2.5 million. After missing his rookie season with a foot injury, Martin started 62 games in the past four seasons in Houston.