Trailing 13-0 against the Broncos, the Titans replaced Mariota in the third quarter after a dreadful start. The former first-round pick completed only 7-of-18 pass attempts for 63 yards. He also threw two interceptions and finished with a dismal 9.5 quarterback rating.
Titans head coach Mike Vrabel told reporters after the game that he will discuss the team's quarterback situation with general manager Jon Robinson and his coaching staff before making a decision on who will start in Week 7 against the Los Angeles Chargers.
"I'll let you know as soon as I figure it out and do what's best for the team," Vrabel said.
The Titans selected Mariota with the No. 2 overall pick in the 2015 NFL Draft out of Oregon. The signal-caller is in the final season of his rookie contract.
Mariota also struggled in the Titans' loss to the Buffalo Bills last week, completing less than 60 percent of his passes with no touchdowns.
"I don't feel great," Mariota told reporters Sunday. "Coach [Vrabel] made a decision, and he's going to make a decision that's best for the team. I respect it, and I just try to be there for Ryan."
In relief of Mariota, Tannehill, a former first-rounder for the Miami Dolphins in 2012, completed 13-of-16 throws for 144 yards but also tossed an interception.