An eccentric former hedge-fund millionaire has gone from living in the Waldorf Astoria to being a missing homeless person that the police are trying to locate safely, The Post has learned.

Paul Greenwald, 70, was reported missing after leaving Bellevue Hospital in Kips Bay at about 2 a.m. on Saturday, police said. He was admitted to the hospital on Aug. 9 for unknown reasons, authorities said.

A hospital camera recorded Greenwald as he walked out, authorities said.

Greenwald, who police said is homeless, recently lived around the corner from the hospital at the Bellevue men’s shelter on East 30th Street, a police source said.

His descent into homelessness marks a stunning fall from his once luxurious lifestyle, which apparently began after a dispute with his estranged wife.

He first got into legal trouble in 2009 — when he was 61 — after attacking his ex-wife, Michelle Greenwald, an NYU professor and cookbook author, The Post reported at the time.

Greenwald, who was living in the Waldorf Astoria Hotel at the time, allegedly lured Michelle to step outside her Horatio Street apartment by phoning her and saying she was parked by a fire hydrant. When she showed up, he grabbed her arm and screamed at her, she told police at the time.

Michelle teaches at NYU’s Stern School of Business and wrote the popular “The Magic Melting Pot” cookbook in 2003.

Greenwald was then committed to Bellevue Hospital’s jail ward after a panel of court-appointed specialists believed he was too sick to knowingly plead not guilty.

At a subsequent court hearing, Greenwald — who was charged seven counts of felony criminal contempt — was dismissed from the court for shouting at the judge. “The judge is a f—ing crook!” he yelled, according to a Post report.

Greenwald was last seen leaving Bellevue on Saturday morning. He’s about 6-feet-tall and weighs 200 pounds and was wearing a red shirt, black pants and black sandals.