Disturbing video shows a disabled man getting knocked unconscious by a construction worker inside the elevator of a Manhattan building – and the victim is now filing suit over the unprovoked attack.

Richard Regen, 60, had been heading to rehab for a stroke he suffered two years ago when construction worker Andrew Caban allegedly shoved him and then punched him twice in his Chelsea building elevator, according to the Manhattan Supreme Court suit filed Tuesday and his lawyer.

The Feb. 2 assault was captured in a video – obtained by The Post – by the West 23rd Street building’s surveillance cameras.

After Caban allegedly lands the knock-out blow, he calmly waits to exit the elevator while Regen lays momentarily unconscious on the vestibule floor, the footage shows.

The brute appears to turn around, say something and gesture as he leaves an incapacitated Regen behind.

For roughly three more minutes, Regen can be seen struggling to get out of the elevator and unable to get himself off of the ground.

Regen was hospitalized for more than a week before he had to undergo brain surgery, according to the lawsuit filed by Regen and his wife, Lili Abir Regen, against Caban and the construction company that employed him, M Daddio, Inc.

“After brutally attacking Regen, … Caban stood over Regen’s body as the elevator descended to the first floor, but offered Regen — who was gravely injured — no help,” the suit charges.

Caban then “fled the premises,” the filing claims.

Prior to the attack, Regen suffered from “a recent neurological injury affecting his ability to communicate,” the lawsuit says. 

Regen family attorney, Nathan Werskman, explained that his client had been in rehab for two years, recovering from a stroke that caused his disability.

That day, Regen had been on his way to an appointment to rehearse a speech for his upcoming graduation from the rehab program, Werksman said.

“This horrific and unprovoked attack against Richard demands justice and accountability for those responsible,” Werksman said. 

“New Yorkers should not fear being attacked in their own elevators by anyone, let alone by the people specifically hired to work on their buildings.”

Werksman claimed the dispute began when Caban – who had been holding the elevator for construction reasons – allegedly rode down to Regen’s floor where the resident had been repeatedly calling the lift.

The two began exchanging words, with Regen telling the worker he wasn’t allowed to hold the elevator, prompting Caban to allegedly threaten, “Do you want to get hit?” according to Werksman.

“I never — in a million years — thought something like this could happen to my husband in our own building,” Abir Regen said in a statement. “Above all else, we hope with this lawsuit to protect other people so it doesn’t happen to them.”

Now, Regen is back in rehab including physical and occupational therapies and he requires round-the-clock supervision – unlike before when Regen was still independent, Werksman said.

The lawyer said his client’s symptoms are “significantly worse” than before the attack.

Caban faces criminal misdemeanor charges over the incident including for assault and harassment, court records show. His next court date in the criminal case is on Wednesday, according to the records.

Regen and his wife Lili Abir Regen are suing for unspecified damages.

Lawyers for Caban and Daddio didn’t immediately return request for comment Tuesday.