Williams' injury comes just two days after 49ers general manager John Lynch announced that presumed starter Jerick McKinnon will be shut down for the remainder of the preseason with a calf strain. He'll be questionable for the team's season opener against the Minnesota Vikings.
The trio of injuries leaves a clouded backfield situation in head coach Kyle Shanahan's high-octane offense. Williams was expected to compete for snaps with McKinnon and Breida. Raheem Mostert, Jeremy McNichols, and newly-signed Alfred Morris will see the majority of carries during the 49ers' final two preseason contests.
Williams was a fourth-round selection in the 2017 NFL Draft. Lynch removed him from his draft board due to concerns over his level of commitment - Williams briefly retired from football in college - but Shanahan and running backs coach Bobby Turner insisted they take a chance on the ball carrier.
Williams missed his rookie season after suffering an ankle injury last September.
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