San Francisco announced the move on Sunday. Sources told NFL Network and ESPN that Foster was arrested on Saturday at the team hotel in Tampa on charges of domestic violence. He is being held without bail.
Foster, 24, was the No. 31 overall pick in the 2017 NFL Draft. The Alabama product has 29 tackles and a pass defensed in six games this season. Foster had 82 tackles and a pass defensed in 10 games during his rookie campaign.
The 49ers battle the Tampa Bay Buccaneers at 1 p.m. on Sunday at Raymond James Stadium in Tampa.