The hapless Jets lost starting quarterback Geno Smith to a locker-room “sucker-punch” Tuesday by teammate IK Enemkpali over a measly $600 debt, sources told The Post.

Smith’s jaw was fractured in two places by the blind-side punch inside the team’s training camp in Florham Park, NJ, sources said — and he’ll be out for six to 10 weeks.

Head coach Todd Bowles said Smith will need surgery after getting “cold-cocked, sucker-punched, whatever you want to call it” by reserve linebacker Enemkpali, who was cut from the team immediately after the punch-out.

Sources said Enemkpali was furious at the star quarterback for failing to reimburse the $600 that Enemkpali shelled out for airline tickets and limos for Smith to attend a July 11 football camp for kids that the fiery linebacker sponsored in his hometown of Pflugerville, Texas.

Smith backed out days before the charity event, following the death of his brother’s best friend in a motorcycle crash, sources said.

Enemkpali gave Smith the silent treatment when the Jets reported to training camp on July 29, and Smith agreed to pay him back when he found out why, sources said.

But Smith, who was set to make $1.7 million plus bonuses this year, never paid the money back, and the players got into a heated argument that ended with the devastating punch, sources said.

Smith, who was knocked to the floor, got up and told Enemkpali, “I’m not doing this here,” then walked away, sources said.

Asked about the reason for the attack during an afternoon news conference, Bowles said that “the whole thing is childish.”

“It was tit-for-tat, he said-she said, high school stuff that they could’ve been handled better than they handled,” Bowles said.

Smith is in the third year of a four-year, $5 million contract. Enemkpali, meanwhile, lost $510,000 in salary he was set to earn.

“Geno Smith” trended on Twitter as news of his injury spread, with many bitterly bidding him good riddance.

“Enempkali punching Geno Smith in the face was the best thing that could’ve happened to the Jets. They might win a few games now. @nyjets,” wrote @MarkFPenguin.

“Gonna sound like a jerk, Geno Smith being out and Ryan Fitzpatrick starting is the best thing for the Jets,” @justinhartling tweeted.

The satirical website Sports Pickle also wrote that Smith’s broken jaw would leave him “sidelined for 18 to 30 interceptions.”

Following his attack, Smith posted a scowling selfie shot in the driver’s seat of an SUV — and showing significant swelling to the right side of his face along with the message, “ILL BE BACK!”

https://instagram.com/p/6QKBL5lBXL/

“My only goal is to heal quickly and get back to playing with my teammates so I can be the best QB possible for the NY Jets,” he later said in a statement released through ESPN.

It was unclear if Enemkpali would face prosecution over the attack. A law enforcement source said New Jersey allows authorities to prosecute assault cases without a victim’s cooperation, but Capt. Robert Treiber of the Florham Park Police Department told NJ.com: “The victim would have to reach out to us.”

“As of now, we haven’t heard anything,” Treiber said.

The Jets have three other quarterbacks on the roster: Ryan Fitzpatrick and rookies Bryce Petty and Jake Heaps.

Fitzpatrick will get first crack at being the starter, but Bowles said the Jets could add another quarterback. Multiple reports later Tuesday cited the Jets’ interest in journeyman Rex Grossman.

In a statement released through his agent, who is ironically also a personal-injury lawyer, Enemkpali said: “I apologize to the Jets organization, coaches, teammates and fans.”

“Geno and I let our frustration get the best of us, but I should have just walked away from the situation,” he added.

“I deeply regret and apologize for my actions. It was never my intention to harm anyone. I appreciate the opportunity I had with the Jets.”

His sister refused to comment when approached at Enemkpali’s parents’ home in Pflugerville.

Additional reporting by Ashley Lauretta in Pflugerville, Texas