Blair needed some assistance getting off the field and was noticeably avoiding putting weight on his right leg. The defensive lineman was examined in the medical tent, and then carted to the 49ers locker room for further evaluation before being ruled out of the rest of the game.
Blair was seen using crutches to get around after the loss with his right leg in a heavy brace.
Head coach Kyle Shanahan told reporters via a conference call on Tuesday afternoon that Blair suffered a torn ACL and will be placed on season-ending injured reserve.
Blair finishes the season with 21 tackles and three sacks through nine games this season, his fourth with San Francisco since the team made him a fifth-round draft pick out of Appalachian State in 2016.
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