Donald Trump has shown little restraint in going after issues sensitive to Hillary Clinton — including discussing her husband’s extramarital affairs and questioning her health — at his campaign rallies. But experts said such attacks may not play as well on the debate stage when the rivals meet later this month at Hofstra University.

The GOP presidential nominee told The New York Times last week that he would “rather not” attack Clinton personally, but he issued the caveat, “If she hits me, though — you have to see what happens.”

Clinton, the Democratic nominee, said she is prepping for the unpredictability associated with her rival and his campaign.

“I’m running against someone who will say or do anything, and who knows what that may be,” she told supporters at an East Hampton fundraiser last week, adding that Trump at the Sept. 26 debate could “try to be presidential” or “try to come in and try to . . . score some points.”

The 90-minute and one-on-one format of the Hofstra debate, the first formal faceoff of the general election, will leave more time to fill and make it harder for Trump to effectively wield the one-liners that worked in the primary debates, said Manhattan-based Republican consultant Susan Del Percio.

“What does Donald Trump consider ‘throwing the first punch’? What he perceives as a personal attack on his intelligence or temperament may unleash him,” Del Percio said.

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Democratic communications consultant Brad Bannon, based in Washington, D.C., predicted that Trump won’t be able to resist.

“I just can’t see him being there next to Hillary Clinton and not beating her up personally,” Bannon said. “I don’t think he has the discipline to stop himself.”

While experts said Clinton could hit Trump on sensitive issues such as his business record or personal finances, she already has been the target of criticism that Trump on the trail has sought to tie to weakness of character.

Last month, Trump brought up Bill Clinton’s 1990s relationship with Monica Lewinsky to supporters in Fairfield, Connecticut, saying the former president was busted by physical proof.

“I’m so glad they kept that dress. . . . Because it shows what the hell they are, all right?” Trump said.

He said in May in Eugene, Oregon, that Hillary Clinton was the “worst enabler” of her husband’s infidelities.

Last month, in West Bend, Wisconsin, Trump questioned Hillary Clinton’s health, saying she doesn’t have the “tremendous physical and mental strength and stamina” necessary to be commander-in-chief. Former New York City Mayor Rudy Giuliani, a Trump surrogate, picked up the unsubstantiated reports of her poor health, citing “several signs of illness.”

However, JuanPablo Andrade, an adviser to Trump’s National Diversity Coalition who is not aiding in the candidate’s debate prep, said he expects both the real estate mogul and the former secretary of state will stick to the substance.

“I really don’t think that the attacks will get personal and I really hope they don’t, because that’s really not want people want,” said Andrade, of Kings Park. “People want to get down to the facts and the issues and what the candidates will do.”

He added of the mudslinging: “We’ve all heard it already.”