Williams was injured when he was being cut block by J.R. Sweezy midway through the quarter on Sunday night. Williams' left ankle was caught underneath as Sweezy made the block on a 2-yard run by Marshawn Lynch. He was down on the field for a few minutes before being helped off by a pair of trainers,Jerseys NFL China, putting very little weight on his left leg.
The 49ers announced later in the quarter that Williams would not return. Williams was replaced in the lineup by Glenn Dorsey, who sacked Seattle quarterback Russell Wilson on the next series.