Jaguars coach Gus Bradley said Gabbert likely will miss Sunday's game at Denver because of a Grade 2 left hamstring strain.
Gabbert suffered the injury in the third quarter of Jacksonville's 34-20 loss to the St. Louis Rams on Sunday. Bradley said Gabbert's status is week to week, so he could miss several games.
Chad Henne will make his third start of the season Sunday if Gabbert is unable to play.
"Haven't heard anything yet, so just like I said last night, just prepare like I'm the starter and we'll see what happens," Henne said.
Gabbert has already missed two games this season because of a cut on the back of his right (throwing) hand, and this is the fourth injury he has sustained since training camp began. He battled a sprained ankle early in camp and fractured his right thumb during the first half of the second preseason game but returned to start the season opener against Kansas City. He cut his hand late in that game and missed the next two contests.
Gabbert has not played well when he's been on the field, completing 48.8 percent of his passes for 481 yards and one touchdown with seven interceptions. He has had an interception returned for a touchdown in each of his three starts. Henne has completed 55.8 percent of his passes for 601 yards and two touchdowns with two interceptions.
Despite that discrepancy, Bradley says Gabbert will remain the starter when he's healthy -- but he's got to play much better.
"We've got to hold everybody accountable," Bradley said. "Blaine, when you look at him on tape where last week I said, 'You know what, he made a lot of his good reads and we've got to make plays for him,' and I felt strong about that.
"I feel strongly [this week] about Blaine, but there was missed opportunities by Blaine this week, and he's got to step up in the pocket, he's got to stay strong, he's got to play with confidence and make those passes that he does in practice. That's the next step for him."
Bradley also admitted that the staff needs to start examining why Gabbert has not been able to stay healthy. He has failed to finish the game in six of his past 10 starts, including the preseason.
"That is something that we have to take a look at, not only within our training and strength and conditioning, but also Blaine," Bradley said. "You've got to be able to trust that he's going to stay healthy and for whatever reason, these things have happened. I know his workouts and he's training and he's doing these things, but we have to take a look at that."
In other Jaguars injury news, Bradley said he doesn't anticipate tight end Marcedes Lewis (calf) being able to play against the Broncos. Lewis has been on the field for only two plays this season. Tight end Allen Reisner has a right MCL sprain and will miss up to six weeks, Bradley said.