ENGLEWOOD, Colo. — As the Denver Broncos’ ground game has cranked up, its red-zone offense has struggled.

“The guys up front have done a heck of a job and we’re looking to find a way to keep moving the ball,” said quarterback Peyton Manning. “The one thing we got to work on coming off last week is finishing down in the red zone with more touchdowns.”

The Broncos’ inability to convert red-zone opportunities into touchdowns against Kansas City kept the Chiefs within shouting distance for much longer than the flow of the game should have indicated.

Not including a kneel-down series at the end of the game, the Broncos crossed the goal line on just one of six drives that reached the Kansas City 20-yard line or closer. And while Connor Barth cleaned up the stalled drives with five field goals in as many attempts, the Broncos’ recent red-zone struggles have dropped them to fifth in the league in red-zone offense.

The absence of tight end Julius Thomas appears to have hurt the Broncos in recent weeks. He has not played since injuring his ankle late in the first quarter of the Nov. 16 loss at St. Louis, and in the games that followed, the Broncos have scored touchdowns on six of 15 red-zone trips, with six field goals, one missed field goal and two game-ending kneel-downs.

Thomas’ nine red-zone touchdowns lead the league, and his deft short seam routes and catch radius provide the Broncos with a unique weapon. Without him, the Broncos struggle to execute similar plays, including one where Manning and tight end Jacob Tamme couldn’t connect on a potential touchdown pass in Kansas City.

“I can’t lie to you and tell you I don’t picture myself making big plays even when I’m not playing,” said Thomas. “So, if I’m in the game, I’m thinking, ‘Ooh, if we could just get this look, or if I was out here on this play I could have probably done something to help my team.’ That’s absolutely how I look at it.”

But Manning does not want to attribute the struggles to Thomas’ absence.

“I can’t point it there. You watch each possession and we had chances in the third one, Jacob and I just missed, (Demaryius Thomas) and I just missed on that one and it could’ve been a third (touchdown) and if you go to the others there was a negative play on a first down, which sets you back.

“Every red-zone opportunity has its own story and nobody wants to hear it they just want to see if you get a touchdown or a field goal. I can’t say that. I think somehow we’ve got to find a way, I’ve got to find a way to help us get into the end zone with Julius or without him.”

But even if Manning doesn’t want to put the struggles at the feet of Thomas’ ankle injury, he knows what the offense lacks without him. And while Tamme can make some catches and tight end Virgil Green is a solid blocker, the offense isn’t quite the same without the threat of the Pro-Bowl tight end.

“When you have one of your top players go out you are going to miss him. Everybody tries to kind of fill that void with Virgil and Jacob,” Manning said. “We hope to get Julius back out there. There’s no question when he’s out there he makes a difference, he makes a lot of plays for us.”

And the Broncos hope that he returns this week. Thomas said the ankle injury is nothing like the one that hindered him for nearly two years after Week 2 of his 2011 rookie season.

“It’s just going to be something I’ve got to work through,” Thomas said.