Romanowski has missed Oakland's last four games after a series of concussions earlier in the season, which ended his streak of appearances in 243 consecutive games. Romanowski, who has played in five Super Bowls, never missed a game before this season.
The 37-year-old Romanowski left the Raiders' training complex before head coach Bill Callahan's announcement. He will remain with Oakland for the rest of the season as an unofficial defensive adviser, helping the team and his replacement, Travian Smith.
Romanowski, in his second season with the Raiders, also played for Philadelphia, San Francisco and Denver. His high-profile career has included plenty of intimidating hits and a fantastic regimen of physical preparation - as well as a history of questionable behavior, including an infamous fight during training camp two months ago.
Last week, Romanowski was sued by teammate Marcus Williams for punching the second-year tight end in the face during the fight. Williams also is on injured reserve with a broken orbital bone.
The suit, filed in Alameda County court, seeks unspecified damages for alleged battery, negligence and intentional infliction of emotional distress. Romanowski has apologized for his actions.
Romanowski has undergone dozens of tests with several teams of doctors in recent weeks to examine his health, and doctors apparently advised him against returning to the field this season. He is expected to visit specialists for several more months before making a decision on his future.
In addition, if Romanowski retires before the end of the season, it would cause serious salary cap problems for the Raiders by accelerating the application of his signing bonus to Oakland's salary limits.The Raiders will consider several options to fill Romanowski's roster spot. Players at several positions will audition this weekend for the team, which is on its bye week.