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NASHVILLE, Tenn. –** Matt Cassel's job description isn't written on his contract, but in his 13th NFL season, he knows the drill.

"You have to be ready at any point in the season to play and perform and be accountable for your team," Cassel, the Titans' back-up quarterback, said on Sunday in Houston. "That's my job."

Cassel, of course, was called into action in the second half against the Texans because of a hamstring injury suffered by starting quarterback Marcus Mariota.

And there's a chance he could be needed again on Sunday when the Titans face the Dolphins.

Coach Mike Mularkey on Monday told reporters an MRI revealed Mariota suffered a strained hamstring, and he's "day to day." His availability for Sunday's game in Miami might not be known until later in the week.

In the meantime, the Titans plan to watch Mariota as he heals while Cassel should see his workload increase in practices.

"Matt will get a number of reps, I can't tell you (how many)," Mularkey said. "I would think Wednesday that would be the case until we see more about Marcus (Mariota). Yeah, that would be the thought process of having Matt (Cassel) take as many reps as possible.

"It is a good locker room, it's a great locker room. They're all behind Marcus, they're behind Matt when he had to go into the game (Sunday). They will rally around Matt. Matt has a great relationships with these guys. I don't see anything negative within the locker room having somebody having to step in and perform as a backup."

Cassel, who's 35, has plenty of experience.

During his career he's played in 104 games, with 80 starts while playing for the Patriots, Chiefs, Vikings, Bills, Cowboys and the Titans.

Cassel joined the Titans prior to the 2016 season, and he started the final game of the season after Mariota suffered a fractured fibula in Week 16 at Jacksonville. The Titans beat the Texans that day, as Cassel completed 16-of-26 passes for 150 yards, with a touchdown and an interception.

Cassel didn't fare as well coming off the bench on Sunday, as he completed 4-of-10 passes for 21 yards in the second half, with two interceptions.

"It was a performance none of us are proud about," Cassel said. "I would have loved to go out there and started a comeback, but obviously it didn't go well. It was a bad day at the office. I have to play better obviously. I have been doing this for a long time and this was one of those things where things went downhill pretty quickly."

Cassel acknowledged it's more difficult coming off the bench in game, but said "there's no excuses."

His plan this week: "Get ready to play."

Mularkey said a week's worth of preparation would make a big difference for Cassel -- if he's needed.

"I was a backup for six years before I became a starter," Mularkey said. "There is a difference when you get to have a chance to do all the reps and you start the game and you get into the flow if the game, it is different. I have never been a quarterback in the NFL, but I would think it would be a lot different when you get a whole week's worth of work and then start the game, you're in the flow."