Investigators suspect Jeffrey Epstein was assaulted in a Lower Manhattan lock-up – and questioned a hulking ex-cop who’s housed in the same unit, law-enforcement sources told The Post on Thursday.

Epstein was placed on suicide watch after he was found sprawled on the floor of his cell, nearly unconscious and with injuries to his neck, the sources said.

But authorities are leaning away from the idea that the convicted pedophile did it to himself, either to commit suicide or merely get transferred out of the infamous Metropolitan Correctional Center, sources said.

“The marks are more consistent with being choked out than hanging yourself,” one source said.

Epstein, 66, has refused to cooperate with investigators, sources said.

Fellow inmate Nicholas Tartaglione, a former Briarcliff Manor cop who faces the death penalty in four drug-related killings upstate, was wearing earbuds when investigators went to question him about the incident, sources said.

Tartaglione, 51, claimed that he didn’t hear anything and wasn’t responsible for Epstein’s injuries, sources said.

Epstein, 66, was found nearly unconscious and sprawled on the floor of his cell in the Metropolitan Correctional Center on Tuesday, sources have said previously.

The multimillionaire financier was rushed to a nearby hospital, where he received treatment before being returned to the infamous jail and placed on suicide watch, sources said.

Earlier this month, The Post exclusively revealed that Epstein was being housed in the “10 South” unit, a block of six cells known as the “terror wing” because it’s where the city’s most dangerous federal inmates, including alleged terrorists, are held.

Tartaglione’s defense lawyer, Bruce Barket, said the beefy ex-cop and Epstein were housed “in the same unit and doing well,” according to NBC News 4, which first reported the questioning of Tartaglione.

In a prepared statement, Barket also said, “Any suggestion that Mr. Tartaglione assaulted anyone is a complete fabrication.”

Barket accused authorities of trying to “retaliate against Mr. Tartaglione for complaining to the court about the deplorable conditions at the MCC.”

“We made those complaints on Monday in open court. We warned the judge that officials at the jail would retaliate against Nick because we have been exposing the inhumane conditions at the facility,” he said.