On Monday, head coach Kyle Shanahan confirmed what he feared after Sunday's loss against the Philadelphia Eagles. Ansah suffered a torn biceps, will have surgery, and land on injured reserve.
Ansah was ruled out at halftime and wasn't on the sideline for the second half of action.
"Went out, probably will have to go to IR," Shanahan said of Ansah after the game. "... Everything that I've heard in there, sounds like that's going to happen. So, pretty sure we'll find that out. Confirm that tomorrow, but that's what it sounded like."
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The 49ers' defensive line has had to endure several injuries. The team was already without Ronald Blair and Jullian Taylor, who are expected to return later this season. In addition to losing Bosa to a torn ACL, Solomon Thomas suffered the same injury in the same game on the same defensive series. In fact, both injuries occurred within three plays.
On Saturday, veteran Dee Ford was placed on injured reserve with a back injury. The 49ers own a next-man-up mentality, but the mounting losses may be too much for the defense to overcome.
San Francisco signed Ansah to a one-year deal on September 23. The Pro Bowl (2015) defender did not record a tackle in his two appearances with the 49ers.
The Lions drafted Ansah out of BYU with the No. 5 overall pick in 2013. He recorded 228 tackles, 50.5 sacks, four passes defensed, and 12 forced fumbles through his seven NFL seasons before signing with San Francisco.