The six-year safety was released by the Detroit Lions last week. Mays signed with the Lions this offeason following his release from the Minnesota Vikings in March.
Mays has started only four games since his rookie season, and tallied 98 tackles and one forced fumble in his career.
The former USC standout has reunited with his former coach college coach Ken Norton Jr. in Oakland.
The latest Around The NFL Podcast discusses Jordy Nelson's knee injury and gives its winners and losers from Week 2 of the preseason.