Now that we’ve found out — with more-than-reasonable certainty — that Christian Hackenberg is not ready to be the Jets’ starting quarterback any time soon (read: Week 1 in Buffalo), it’s time for the Jets to get down to the business at hand.

That means getting veteran quarterback Josh McCown ready to start the season and by honing their defense into what it needs to be, which is the heart and soul of this offensively challenged team.

The Jets defense is the only element of their team that has a chance not necessarily to win games for them but simply to keep them in games and keep them competitive. After watching the Jets beat the Titans 7-3 in their preseason opener last week and lose 16-6 to the Lions on Saturday night at Ford Field, you cannot help but wonder how they’re going to score an offensive touchdown this season.

When coach Todd Bowles was asked after Saturday night’s loss, in which he started Hackenberg and watched him complete 2-of-6 passes for 14 yards in the first half and get sacked twice for losses of 17 yards (for those of you scoring at home, that’s minus-3 net passing yards), if he was ready to name McCown as the opening-day starter, the Jets coach said: “Not at this point.’’

Even though — despite Bowles’ attempt to be coy — we all know McCown is the starter, one thing we don’t need to be told about this team is the fact that its defensive players must take on the onus as the leaders.

Is this fair? Of course not. But it’s the Jets’ reality in 2017. The defense has more talented, more accomplished, more experienced players than the offense does — and that is saying something when the two starting safeties are rookies Jamal Adams and Marcus Maye.

“The backbone of this team is going to be the defense, so we’ve got to perform at a high level every time — no excuses,’’ linebacker Demario Davis said after the game. “It’s a challenge, and we accept the challenge. We embrace the challenge.’’

Providing the defense, led by its strong line of Leonard Williams, Muhammad Wilkerson, Sheldon Richardson and Steve McLendon, doesn’t cave under the weight of the team’s anemic offense, one of the challenges will be not pointing fingers at the offense for not pulling its weight.

Asked if he believes the “onus’’ is on the Jets defense, cornerback Morris Claiborne said, “Definitely.’’

“We feel like it’s all on us as a defense,’’ he said. “We feel like we have to go out and help our offense, go out and take the ball away, try to steal possessions for our offense. We feel like we need to score on our own. So we definitely feel a lot of pressure. But I don’t think it’s anything we can’t handle.’’

Richardson said the defensive players “are very aware’’ of the team’s offense trying to find itself with so many inexperienced players.

“No matter what position the offense puts us in, we’ve got to stop [opponents] — field goals included,’’ Richardson said. “If offense isn’t scoring, the defense has got to make something happen.’’

While these things are difficult to measure in preseason with teams evaluating their talent, the Jets defense has allowed just 19 points in two games, including only one touchdown, which came Saturday.

“Not good enough, because we hold ourselves to a higher standard,’’ Adams said.

“Not up to our standards. We’ve got a lot more improvement to do,’’ Maye said.

“We’ve all got to get better and come out faster on both sides of the ball,’’ Wilkerson said. “We came out a little slow. We’ve got to do a better job next week.’’

Saturday is the annual Jets-Giants game at MetLife Stadium, the manufactured “Snoopy Bowl.’’ The third preseason game traditionally comes as close to mirroring a regular-season game as any of the summer exhibitions. That means a lot of McCown at quarterback to get him ready for Buffalo and beyond and better defense.

“It’s not any extra pressure,’’ Maye said. “We know where we want to be and what we’re capable of as a defense. We know what we have to do as a defense, and we know the situations that we have as far as the offense goes. We’ve just got to out there and do our job and create as many opportunities as we can for our offense. It’s a team effort.’’

Except the Jets, with their uncertainty at quarterback and dearth of skill position players, look a lot like one half of a team right now.