In danger of losing three straight for the first time in four seasons, the Denver Broncos face their former coach without their future Hall-of-Famer under center.
A season that looked promising has become concerning for Denver, which followed a 7-0 start by dropping two straight for the first time since September 2012 - the season after the Broncos last lost three in a row.
They'll try to avoid doing it again without Manning, who was benched last Sunday after throwing four interceptions in a 29-13 loss to Kansas City. A day later the Broncos announced that Manning has a torn plantar fascia in his right foot and coach Gary Kubiak decided to hand the offense over to Osweiler.
Kubiak second-guessed himself for playing the hurting 39-year-old, who came into the game against the Chiefs with a ribcage injury and sore shoulder.
''Guys want to play,'' Kubiak said. ''That's why he's a great player. But as a football coach, sometimes you have to say, 'No, I don't think this is the right thing today.'''
Those injuries have contributed to Manning enduring perhaps the worst of his 17 NFL seasons - a career-low 67.6 passer rating, 59.9 completion percentage and 17 interceptions to nine touchdowns. However, he's started every game since coming to Denver in 2012 and last missed one while sitting the entire 2011 season after neck surgery.
That changes Sunday when Osweiler, 31 of 54 for 305 yards with two TDs and an INT in 15 games over four seasons, starts on his 25th birthday.
''That would be an awesome birthday present if we can go get a win,'' Osweiler said. "It's very exciting, but at the same time Peyton is still our guy. He's one of the best ever to do it.
''I'm the starter for this week at Chicago, but that's all it is."
Kubiak hasn't announced a timetable for Manning's return.
"All of our full attention is going to be to getting Peyton back and healthy,'' he said. "We're focused on this week, then we'll re-evaluate next week.''
Osweiler will try to revive an offense that totaled 221 yards and committed five turnovers while scoring its fewest points of the season last weekend. Whether it's Ronnie Hillman or C.J. Anderson running the ball, Denver ranks 29th in rushing, averaging 86.0 yards and has gained 104 in the losses to Indianapolis and Kansas City.
Things might not get easier against Chicago (4-5), which is looking for its first three-game winning streak in two seasons. Guided by Fox and offensive coordinator Adam Gase, who were together in Denver the last four seasons, the Bears are 3-0 against the AFC West.
"Yeah, coach Fox knows a lot about us, but we also know a lot about him," Osweiler told the Broncos' official website.
From 2011-14 with Denver, Fox went 46-18, won four division titles and reached the Super Bowl once. Four days after the Broncos and Fox mutually parted ways in January, he accepted a four-year deal to coach the Bears and brought Gase with him.
Naturally, Fox is downplaying the reunion.
"When you've been doing this for 26 years, you kind of run into a lot of people you know,'' Fox said. ''When you're with your eighth team, you end up playing your ex-team a bunch.
"I have a lot of close friends (in Denver), a lot of people I've shared special moments with but it's the next team on the schedule."
And one the Bears should feel confident to face after recording consecutive road victories over San Diego and St. Louis.
''Nameless and faceless, that's how we look at (opposing) guys,'' Chicago linebacker Shea McClellin said.
After allowing an average of 35.0 points during an 0-3 start, the Bears are yielding 21.5. Chicago gave up a seven-play, 80-yard scoring drive to open Sunday's game, then held the Rams to 205 yards and two field goals in the 37-13 rout. The Bears did so without linebacker and defensive leader Pernell McPhee, who could miss a second straight game with a knee injury.
''The way we are trending, I like the way the guys are going about their business,'' Fox said.
Ex-Bronco Jay Cutler threw three touchdowns without an interception last week. Under Gase's tutelage, Cutler has thrown at least one of his 13 TDs in each of the eight games he's played and only two of his five INTs in the last five.
"I think he's playing the quarterback position exceptionally well,'' Fox said of Cutler, whose 95.3 passer rating is a career high.
Rookie Jeremy Langford has rushed for 145 yards, caught 10 passes for 179 and scored three TDs while replacing the injured Matt Forte (knee) the last two games. It's uncertain if Forte will return to face a Denver defense that's allowed 56 points in the last two contests after yielding an average of 16.0 in the first seven.
The Broncos rank first in total defense (277.3 yards per game) but have allowed 668, including 226 on the ground, in the last two contests.
Denver will have cornerback Aqib Talib back after he served a one-game suspension for poking Indianapolis' Dwayne Allen in the eye. Safety T.J. Ward, meanwhile, won't be suspended after being ejected for taking a swing at Kansas City's Jeremy Maclin.
DeMarcus Ware, who has a team-leading 6 1/2 of Denver's 32 sacks, could sit a second straight contest with a back injury.