Chad Henne is replacing Blaine Gabbert in Jacksonville as the Jaguars are getting beat down by the Houston Texans. Gabbert has an ice pack on his left thigh so it's actually an injury that's giving Henne his shot.
It's unclear exactly what the injury is or whether it's serious. Henne was brought on as a backup in the offseason, one of the better backup options in the league.
Gabbert has not looked great in the Jaguars game, completing only 7-of-19 passes for 53 yards and a touchdown. You couldn't blame the Jaguars if they decided to make a change at quarterback, injury or not. No interceptions is a good start for Gabbert but averaging less than three yards per completion is not.