Ford had been listed as questionable initially before being ruled out on Saturday for Sunday's game. The team also announced that offensive lineman Hroniss Grasu has been promoted from the practice squad to the active roster.
Ford played only 22% of the defensive snaps in his first season in San Francisco because of various injuries but had a big impact on the pass rush when healthy.
Grasu started at center last week in place of the injured Ben Garland before being sent back to the practice squad. He provides depth on the offensive line, with Garland set to return from a sprained ankle.
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