An offensive line might be the most overlooked unit on an NFL team. But for the Broncos, one could argue it’s the most important. Without solid blocking, Peyton Manning’s health becomes at risk.

Manning lost both of his centers during the offseason as J.D. Walton and Dan Koppen suffered season-ending injuries. Pro Bowl left tackle Ryan Clady saw his season end prematurely after week two. And now, just as the line seemed to be figuring it out as a group, right tackle Orlando Franklin looks to be out for at least a few weeks.

With Franklin out, longtime guard Chris Kuper figures to enter the lineup. Kuper was once a top lineman alongside guys like Tom Nalen and Matt Lepsis. But he hasn’t played in a meaningful game in nearly a calendar year.

In a stretch of about a month, the Broncos have gone from having maybe the best offensive line to one with question marks. One can only hope that Franklin will be back soon and that, until then, his buddies can do just enough to keep PFM upright.

The Broncos did very little against the Jaguars to prove that they’re in prime shape to beat the Colts in a homecoming for Manning. Amazingly, the Jags were within two points at halftime and were within two scores late in the fourth quarter.

As much as I want to give Jacksonville credit, I can’t. I get that Justin Blackmon is a freak and that Paul Posluszny makes plays against anyone, but their team had no business staying in the game with Denver.

You can’t tell me that a team allowing first downs via personal fouls, trying fake punt attempts on their side of the field and being unable to hold a ball during a field goal should win an NFL game. And yet through more than two quarters, the Jags threatened to be responsible for the largest upset in league history.

But the Broncos gave them plenty of help. Although the Jags’ defense didn’t record a sack, they hurried Manning more than any team had in 2013. And when PFM wasn’t pressured, he seemed to be getting low snaps from center Manny Ramirez, two of which resulted in a fumble and turnover.

All three of Denver’s running backs also had issues. Knowshon Moreno may have found the end zone three times, but also had several critical drops, as did Montee Ball. Ronnie Hillman showed he’s still afflicted with fumble-itis after his mistake led to another turnover.

Manning himself had his worst statistical game of the year. He failed to reach the 300-yard mark and threw his second interception in consecutive weeks. PFM even seemed unsure of himself at times, as evidenced by the countless short passes to running backs.

The Colts provide the most challenging matchup for the Broncos up until now. Despite their lack of passing yards, they had a top five offense before their Monday night game with San Diego. Running back Trent Richardson gives Andrew Luck an outstanding complement to the passing game, which features an underrated duo of Reggie Wayne and T.Y. Hilton.

Defensively, the Colts are even better. They rank fifth in points allowed (16.3) and fifth in pass yards (205.7). As out of sync as the Broncos’ offense was against the Jags, they still put up 35 points. The game Sunday will be another chapter of the unstoppable force versus the immovable object.

Three keys to the game for Denver:

1. Von’s back! A week after Dez Bryant exposed the Broncos’ secondary, Blackmon did the same thing. Von Miller may be a knucklehead, but he’s one of the top playmakers in the league. A productive Miller is the perfect antidote for a mediocre secondary.
2. Take care of the ball. The Colts rank as one of the best in turnover margin. One way to avoid the turnover is controlling Robert Mathis, who has recorded nine and a half sacks through six games. If Chris Clark can neutralize Mathis the way he did with DeMarcus Ware, the Broncos breathe a little easier offensively.
3. Peyton’s emotions. The Colts plan to honor Manning in a pregame tribute. Manning must somehow deal with being the opponent in a place he called home for 15 years. I think PFM will definitely show some pregame jitters with some overthrows and maybe an early interception (he’s descended back to planet Earth the last two weeks), but he’s too much of a perfectionist to let the pregame festivities get the best of him.

My prediction: Broncos-31, Colts-28