NFL teams can collapse after losing QB; AFC West open?

ENGLEWOOD, Colo. -- What if this is it for Peyton Manning? While many of his teammates won't dare consider the notion, at least one prominent member of the Denver Broncos has considered the possibility that No. 18's 18th NFL season could come to a premature end.

"I'm not going to lie, I've pondered it a little bit," leading tackler Brandon Marshall said. "But I try not to think about it too much because I know we've got a job to do, I know we've got a season to finish and he's one of the greatest of all-time, man. And I just hate to see him hurt."

Manning's streak of 57 consecutive starts for Denver, a franchise record, will come to an end Sunday in Chicago because of injuries and ineffectiveness. Backup Brock Osweiler gets his first NFL start, which comes on his 25th birthday.

Coach Gary Kubiak excused Manning from practice and meetings this week so he could focus on his rehab on his left foot, right shoulder and ribs. He's also leaving Manning back in Denver so the five-time MVP can continue his treatment through the weekend alongside star pass-rusher DeMarcus Ware (back) rather than having to stand in the cold at Soldier Field.

Manning had the worst game of his career last weekend on the same day he became the league's all-time passing yards leader in Denver's 29-13 loss to Kansas City. He now has 71,871 yards to Brett Favre's 71,838, but he's still tied with Favre for most regular-season wins by a QB with 186.

Nobody knows for certain if he'll get a shot at No. 187.

While Kubiak has refused to look beyond Sunday, there's a distinct possibility Manning could be sidelined for a while given his many ailments at age 39. Osweiler's superior mobility, athleticism, arm strength and accuracy might also give the Broncos (7-2) the boost they've been searching for on offense all season.

Osweiler insists this is still Manning's team and he's only filling in temporarily, which seems to be the prevailing mood in the locker room.

"In this game you learn to work week by week," wide receiver Bubba Caldwell said. "So, I know the mind-set here is we just worry about one week at a time. Against Chicago, we know he's not going to be there. We've got Brock. So, after this game, then we'll worry about the next week and see who our quarterback is."

Manning has had a difficult season. After taking a $4 million pay cut over the winter, he's thrown for just nine touchdowns with an NFL-high 17 interceptions. In his first three years in Denver, he totaled 136 TD throws and just 36 interceptions.

His career-low 67.6 passer rating is even lower than Tim Tebow's 72.9 in 2011 that forced GM John Elway to go after Manning in free agency.

"I just hate to see all these people saying all these negative things about him," said Marshall. "He's had a tough year. It hurts me. I definitely have thought about" this being it for Manning. "But I'm hoping that we can win one for him - a Super Bowl for him - so he can go out in style."

Whether Manning or Osweiler is running the offense, Marshall is counting on Denver's No. 1-ranked defense and top-flight special teams to lead the Broncos out of their two-game skid and back into another nice winning streak.

"Defense wins championships," Marshall said. "Man, if we all just play sound - no turnovers, no big plays - I think we can win every game."

Asked this week if he was confident he'd be back in action soon, Manning said, "I sure hope so. ... I'm not going to be on the practice field, so I can dedicate the time to being in the training room and active rest, if you will. Hopefully, it helps me out."

Manning demurred when age was raised as a possible root of his long list of nagging injuries.

"That's a little bigger of a picture than what I'm dealing with right now," Manning said. "I'm kind of focused on the small picture of trying to get healthy."

Osweiler isn't looking at the bigger picture either.

Although there's a lot riding on this start - he's set to become a free agent after this season - Osweiler insists he doesn't view this opportunity as an audition.

"I'm really keeping my focus small," Osweiler said. "I'm focusing on the things that got me to this point and just focusing on going into Chicago and doing whatever it takes to get that win."

Bears coach John Fox suspects we haven't seen the last of the iconic quarterback he coached for three seasons in Denver.

"He'll bounce back. He's a consummate pro," Fox said. "He'll have better days to come."

. . . .

So Peyton Manning is out. So is Andrew Luck. Tony Romo is finally ready to come back, after the Cowboys went 0-7 without him.

Losing an elite quarterback can be devastating to a team. No one knows that better than the Arizona Cardinals. They are the poster child for how things can head south in a hurry when the main man goes down.

Since the midpoint of the 2013 season, the Cardinals are 20-4 when Carson Palmer starts, 5-6 without him.

Palmer missed 11 games last season, the last five after tearing an ACL. He was 6-0 as a starter. In those games, Arizona averaged 25.8 points per game. Without him, the Cardinals scored 12.9 per game. They finished 3-4, losing to the Panthers in the playoffs.

"It's demoralizing when you lose your franchise player, the leader of your team," Arizona wide receiver Larry Fitzgerald said. "There's nobody more important than your quarterback on your football team, especially when you have an elite quarterback like we do. It takes a while. It's really frustrating. It demoralizes your team."

Arizona didn't just lose its starting quarterback. Backup Drew Stanton went down with a knee injury, too. Arizona signed Ryan Lindley from the San Diego practice squad to start the final three contests, all losses.

Coach Bruce Arians believes the team can keep playing at a high level with Stanton. But he said quality backup quarterbacks are "really hard to find."

Nobody has to tell Dallas Cowboys fans that. Dallas went 0-7 after Romo broke his left collarbone. They lost the first three with Brandon Weeden at quarterback, then they signed Matt Cassel and lost four more.

When Romo was ready to return, the Cowboys gave up on Weeden. He was released and signed by another team with quarterback injury issues, the Houston Texans.

When the quarterback is hurt, the team's defense feels it.

"If you don't have your starting quarterback naturally a lot of pressure does fall on the defense," Arizona safety Tyrann Mathieu said, "to swing field position, force more turnovers, do everything 'extra.'"

Arizona's defense seemed to wear down under that load last year.

"Yeah, it was a lot," Mathieu said, "... Defensively you want to go out there and score touchdowns and make plays and just be an offensive guy. It definitely puts a lot of pressure on a defense, especially as the season goes on and the games get bigger and tougher."

Teams talk about having a good backup quarterback. But there's a reason they are backups.

"You always want to be able to absorb injuries throughout your football team," Cowboys executive vice president Stephen Jones said on his weekly radio show. "If something happens to this guy, put the next guy in and let's go. The best teams are able to do that."

Luck was rarely his old self this season amid rumors he was hurt worse than he or the Colts let on. Now he is gone for perhaps five weeks with a lacerated kidney and abdominal muscle injury. So Indianapolis will turn to 40-year-old Matt Hasselbeck, who quarterbacked the Colts in two wins earlier this season.

"I guess I've been doing this long enough you expect the unexpected," new Colts offensive coordinator Rob Chudzinski said. "That's what this job is and that's what coaching is, is a challenge. It's all about challenges. You look at it like it's a jigsaw puzzle. It can come together and it's a matter of getting those pieces and putting it all together, but it can be done. We'll find a way to get it done."

And in Denver, Manning - one of the best to ever play the position - has been far from his prolific self this season. Now he's been sidelined with a foot injury in favor of untested Brock Osweiler, who has thrown 54 passes in his NFL career.

"To hear coach (Gary) Kubiak say, 'Hey Brock, you're going to start this week at Chicago' in front of the whole team, yeah," Osweiler said, "it's a little abnormal."