Marcus Mariota (ankle) carted off after sack; won't return vs. Jags

— -- JACKSONVILLE, Fla. -- Tennessee Titans quarterback Marcus Mariota was carted off Jacksonville's EverBank Field with a right ankle injury after being sacked from behind by  Jaguars DT  Sheldon Day in the third quarter Saturday.

Mariota left with a portable cast on the ankle and has been ruled out for the remainder of the game.

Matt Cassel, the Titans' backup, came on to replace him.

At the time of the injury, the Titans trailed the Jaguars 25-10 late in the third quarter. 

Protecting Mariota was a huge priority of the Titans in his second season. They signed free-agent center Ben Jones and drafted right tackle Jack Conklin eighth overall and have been a good pass-protecting team all season.