Two games behind both the Oakland Raiders and the Kansas City Chiefs, the Denver Broncos won't be repeating as AFC West champions. Their path to a second straight Super Bowl title will have to come from a wild-card berth.

However, that's no lock for the 8-4 Broncos. One of Oakland and Kansas City are all but guaranteed one of the wild-card spots, and with the Pittsburgh Steelers, Baltimore Ravens, and Miami Dolphins all at 7-5, the reigning Super Bowl champions can't afford a slip-up.

Unfortunately, they face an underrated Tennessee Titans team on Sunday that's fully capable of pulling off the upset.

Here are three reasons why they can:

No Brandon Marshall

Linebacker Brandon Marshall isn't the most valuable member of the Broncos' defense, but the team will feel his absence in Sunday's game.

Second-year player Corey Nelson will likely replace Marshall in the lineup and he'll be forced into some nightmare matchups. Delanie Walker is one of the most productive tight ends in the league, and he should be able to take advantage of Nelson's inexperience. When Nelson isn't covering Walker, he could be asked to spy on quarterback Marcus Mariota. Yeah, good luck with that.

The old adage goes "You're only as strong as your weakest point," and the Broncos' stellar defense could find that out the hard way versus the Titans.

Murray magic vs. Denver's Achilles' heel

Denver, for all its spectacular play on the defensive side of the ball, has struggled mightily stopping the run this season. They give up 122.8 yards per game, ranking 28th in the league. Enter Titans running back DeMarco Murray, who is the focal point of the league's third-best rushing attack.

The Titans won't be able to win just on their ground game, but the Raiders showed how vulnerable the Broncos can be to run game in Week 9, when Latavius Murray rushed for 114 yards and three touchdowns, and Oakland totaled 223 yards on the ground.

And Latavius isn't on DeMarco's level.

He should be able to help the Titans control the clock and wear down the dangerous pass-rushers of Denver, freeing up Mariota and limiting the potential for turnovers.

If DeMarco gets going, the Broncos might not have an answer.

A less than 100 percent Siemian

Trevor Siemian is reportedly set to return to the starting lineup after missing one game with a foot injury. The ailment was severe enough that it was believed Siemian could miss multiple games, but he is apparently good to go.

However, if Siemian isn't 100 percent healthy, it could give the Titans the advantage.

Tennessee's secondary has been its Achilles' heel this season, but Siemian may not be able to take the chances the Titans give him. He missed Week 5 with a shoulder injury and had arguably the worst game of the season a week later, throwing an interception and fumbling twice (losing one) against the San Diego Chargers.

If Siemian is unable to hit the big plays in the passing game, it will be hard to keep up with the explosive Titans offense. And if Paxton Lynch is forced into the game, the Broncos could be in real trouble. The rookie showed in his second career start last week that he can't consistently push the ball downfield.