He threw four interceptions -- including three in the fourth quarter -- for the first time in his three years with the Broncos. After the game, reporters asked if he was having problems with his thigh, for which he skipped practice earlier in the week in order to receive treatment.
Manning denied that was the case, but speculation continues today. Regardless of the reason, though, the future Hall of Famer definitely struggled.
And when Manning struggles, the Broncos struggle. It's a case of bad timing for Denver, which could have sealed a first-round bye with a win over the Bengals but now faces an uneasy week before learning its postseason plans.
Manning also didn't look like himself two weeks ago, throwing for no touchdowns and two interceptions with a season-low passer rating of 56.9 as the Broncos held on for a 24-17 win over the Buffalo Bills.
The reality is that Manning, while still an elite quarterback and one of the all-time best, isn't the quarterback he was even a year ago, when he threw for an NFL-record 5,477 yards with 55 touchdowns and 10 interceptions for a passer rating of 115.1.
Back then, he passed for more than 300 yards in 12 games and 400 yards or more in four, with more touchdowns than interceptions in every game. This year Manning has thrown for 4,143 yards with 37 touchdowns and 11 interceptions for a 106.4 passer rating -- all very good numbers.
But he has thrown for more than 300 yards only six times this season, and only once in the last five weeks. Plus, he's thrown more picks than touchdowns in three of the last six games.
So is it an injury? Age? A fluke? Or nothing to be concerned about?
The Broncos, already the champs of the AFC West, still control their own destiny -- a win over the 3-12 Oakland Raiders in Week 17 will give them the No. 2 seed, a week off and at least one home playoff game.
All advantages they likely will need if they are to advance out of the AFC again this year.