Thomas has torn his anterior cruciate ligament twice in recent seasons, but returned last season to start seven of 16 games played.
He recorded 67 tackles, one sack, one forced fumble and one interception.
For his career, Thomas has 298 tackles, 12 interceptions and seven sacks.
He's a formed second-round draft pick from USC.
The Raiders have signed former Giants pass rusher Justin Tuck already.
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Aaron Wilson covers the Ravens for The Baltimore Sun