Tennessee’s comeback effort against the Texans just got more difficult. The Titans, trailing 37-14 in the third quarter, will be without starting quarterback Marcus Mariota. The third-year passer left the game with a hamstring injury and did not return to the game.

He’s scheduled to have an MRI to determine the severity of the injury. His status for next week’s game against the Dolphins is up in the air.

Mularkey said Marcus Mariota will undergo an MRI on hamstring. Said he injured it on his second touchdown run@Titans — Jim Wyatt (@jwyattsports) October 1, 2017

Mariota suffered the injury on a non-contact play, stoking fear the pain could be anything from a strain to a more serious tear. Matt Cassel, who won his only start for the Titans last season — a meaningless game against the Texans, coincidentally, has been inserted in his place.

What this means for the Titans: Tennessee will have to hope Mariota’s injury isn’t serious. The young quarterback is the jewel of the franchise’s rebuild and its best hope to snap an eight-year playoff drought. Cassel is an inoffensive backup who completed less than 59 percent of his passes last season. He can handle spot duty without costing the team in the long run, but an extended stretch with Cassel as starter would sink the Titans’ playoff hopes.

That’s especially true given the way the defense has played in Houston. Tennessee gave up a point per minute on the road en route to what looks like a Week 4 defeat. At the very least, it will take the pressure off a Mariota return Sunday afternoon.

What this means for Marcus Mariota: Mariota suffered his second lower-body injury in his past five games for Tennessee, and a decrease in mobility would limit the dual-threat skill that’s made him so dangerous in the NFL. Even a minor hamstring strain could keep him from being the kind of dynamic scrambler the Titans have built their roster around.