Bosa was being evaluated for a head injury he suffered in the second half as the Chargers attempted to hold off a Bengals rally.
Coach Brandon Staley said after the game that Bosa did not have a concussion but was held out the rest of the game anyway.
Bosa has battled injuries through much of his career, and usually plays through them. This one was a different story, and the Chargers defense struggled in the third quarter without him.
This season, the 6-foot-6, 280-pound Bosa has 36 solo tackles and 19 assists to go along with 7.5 sacks. In his absence, Kyler Fackrell took over.
The Chargers, at one point up 24-0 over the Bengals, saw their lead shrink to 24-22 in the third quarter before a defensive touchdown turned the momentum toward the road team once and for all.