The California man who was hit with federal charges for allegedly attacking a flight attendant on an American Airlines flight reportedly suffered a traumatic brain injury during an assault in New York City.

Brian Hsu, 20, was accused of slugging the crew member in the face after she told him to sit down because the “fasten seatbelt” sign was on during the Oct. 27 flight from JFK Airport to John Wayne Airport in Santa Ana, according to an FBI affidavit.

The incident took place as Hsu, who attended school in New York, was returning home after undergoing brain surgery, according to the feds.

The suspect claimed he has psychological damage and “brain fog” after being assaulted last fall in Manhattan, according to the Daily Mail.

Police confirmed to The Post that Hsu was attacked by a street peddler selling CDs on Sept. 23, 2020 at Union Square West.

Hsu was diagnosed with brain trauma at Bellevue Hospital, the Daily Mail said.

Hsu claimed to investigators that the flight attendant caused the injury herself when she charged at him and slammed her nose into his palm after he accidentally bumped into her while stretching in the corridor.

The flight attendant was removed from the plane by stretcher after feeling dizzy and was taken to the hospital, where doctors told her that she suffered a concussion.

Hsu’s mother, who was on the plane with him, said he had become easily agitated since his brain surgery and that he had trouble sitting still.

During the flight, Hsu reportedly said he needed to use the bathroom, but was told it was occupied and that he could not wait in the aisle, the federal affidavit said.

That’s when he allegedly went berserk, elbowing the flight attendant in the head before charging at her and socking her in the head, according to the feds.

Four witnesses told investigators that the flight attendant “hit the lavatory door” after she was punched, the report said. The woman also said she suffered a “fractured nose” after the blow, one witness recalled.

Hsu was charged with interference with a flight crew and assault, according to federal prosecutors.

He was released on a $10,000 unsecured bond by US Magistrate Judge Autumn Spaeth, who ordered him to appear in Denver on Nov. 15 for a hearing and directed him to submit to a mental health evaluation, according to Reuters.

Hsu also has been banned from flying on American Airlines.

Airlines have experienced a surge of incidents involving unruly passengers during the COVID-19 pandemic, with thousands reported to the Federal Aviation Administration.

Through Oct. 25, there have been 4,941 reports of unruly passenger incidents, including 3,580 related to face-covering regulations.

In June, a group representing major US airlines as well as aviation unions asked the Justice Department to prosecute violent air passengers.

Additional reporting by Amanda Woods