Mariota, who signed a two-year, $17.6 million free-agent contract with the Raiders last March, was scheduled to make $10.625 million in base salary in 2021 while carrying a salary cap number of $15.35 million.
NFL Network was first to report the restructured deal, a one-year contract worth $3.5 million that could top out at $8 million if incentives are met.
The 2014 Heisman Trophy winner and the No. 2 overall pick of the 2015 draft, Mariota dealt with myriad ankle and shoulder injuries in training camp and started the season on injured reserve.
He appeared in one game for the Raiders last season, replacing an injured Carr in a Week 15 overtime loss to the Los Angeles Chargers while throwing for 226 yards and a touchdown, with an interception, in completing 17 of 28 passes. He also rushed for 88 yards and a TD (with eight first downs) on nine carries.
Mariota, 27, has been the subject of much trade and/or cut speculation this offseason, but the QB market seems to have dried up as of late.