This may not be a must win this Sunday against the Chargers.

But at the very least, this is the Broncos’ first gut check of the season.

The Broncos just blew a huge opportunity by losing to the New York Giants last week. The then, 0-5 Giants.

Instead of being in great shape at 4-1, the Broncos are facing a daunting schedule where they play three straight road games and won’t be favored in their next four.

“We were supposed to win last week, we didn’t win,’’ said Broncos’ pass rushing linebacker Von Miller. “It’s a competitive game. They came out there and did what most people thought they wouldn’t do. I definitely thought they wouldn’t do it. We prepared like it was a great game and we ended up losing. Now you have another Chargers team that has been playing great lately. We have to be desperate this week for the win or it just won’t happen.’’

The way to look at whether a game is truly “must win” is to consider the consequences if the team loses. Never mind how much a division game counts in end-of-year tiebreakers. This is about the quest for 10 wins. If the Broncos lose Sunday, they’re 3-3. Then they play at Arrowhead Stadium on Halloween Eve against the Kansas City Chiefs, who are already a 6 1/2-point favorite.

Then the Broncos play at 5-1 Philadelphia on Nov. 5. Then the Broncos come home to play Tom Brady and the Bill Belichick-coached New England Patriots. Goodness.

Add that up and if the Broncos lose Sunday? They are in trouble. No doubt, they must beat Philip Rivers and the Chargers. Not only are the Chargers 2-4, they’ve lost 7 consecutive home games dating back to San Diego and Qualcomm Stadium.

They are 0-3 at their temporary home of the StubHub Center in Carson, Calif., where their attendance has been 25,381 per game – one third of what the Broncos draw for their home games at eventually-to-be-renamed Sports Authority Field at Mile High.

“I heard it’s been pretty opponent friendly in there,’’ Talib said. I think I saw that (other teams) had a bunch of fans there so I don’t know. We always have a bunch of fans at the Chargers game, so it probably won’t be any different this game.”