Medical staff quickly attended to the rookie, who was able to walk slowly to the sideline under his own power. However, Williams did not return to the field and later exited the practice area accompanied by team personnel.
Head coach Kyle Shanahan addressed the media following practice and said that Williams underwent a "good exam."
"Hopefully, just hyperextended his knee," the coach said. "So, we're gonna get a further evaluation now, but looked good when we examined him."
Shanahan added that he no longer expects Williams to play on Saturday during the 49ers' preseason opener against the Broncos.
"I would be surprised if he went Saturday," Shanahan said. "I mean, we were going to play him, but I've got to see what happened in there. But usually, when you hyperextend your knee, it's going to take at least a couple of days, probably a week."
This will be something worth monitoring in the coming days.
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