Titans head coach Ken Whisenhunt confirmed Friday that Mariota will sit out, even though the rookie said his left knee has been feeling better.
Mariota returned to the practice field Wednesday for the first time since spraining the MCL in his left knee. He was limited in practice this week while wearing a knee brace.
"Marcus Mariota made a lot of progress this week, but we aren't going to play him Sunday," Whisenhunt said.
Mariota suffered the injury on a low and late hit by Miami Dolphins defensive end Olivier Vernon in the Week 6 loss. Vernon was fined $37,363 for two separate hits on Mariota during the game.
Mettenberger completed 22 of 35 passes for 187 yards and one touchdown with two interceptions last Sunday in the Atlanta Falcons' 10-7 win over the Titans at Nissan Stadium.