X-rays were negative and the team did not know how serious the sprain was.
Asomugha is expected to undergo an MRI on the ankle Monday, a source told ESPN NFL Insider Adam Schefter.
Asomugha went down defending a deep pass to Seahawks wideout Golden Tate in the fourth quarter Sunday.
Asomugha was in noticeable pain was unable to walk off under his own power. He went immediately to the locker room.
Information from The Associated Press contributed to this report.