Asomugha, 32, spent eight of his 11 NFL season with the Raiders and rejoined the team for a day Friday to announce he was hanging it up.
Asomugha represented the Raiders at the all-star game three times. He signed a jackpot contract with Philadelphia in 2011, but struggled on the field and was released. He caught on with San Francisco this season but was waived last month.
Off the field, Asomugha married actress Kerry Washington in June. The couple are expecting their first child this year, E! Online said.