Jeffrey Vanchiro, who has gained widespread attention as a colorful and outspoken fan of the Nets, was on a ventilator late Sunday afternoon and was not expected to survive after falling from a second-story window in Flushing, Queens, on Saturday night.

Vanchiro’s fiancée, Kristi Evans, who was with Vanchiro’s family at New York Hospital Queens on Sunday, said that Vanchiro was sleeping at his father’s home on Saturday night. In an interview at the hospital, Evans said that Vanchiro’s father told her that Vanchiro awoke apparently disoriented and leapt from the building. She said that Vanchiro sustained severe brain damage and a fractured spinal cord in the fall, and that his brain had stopped functioning Sunday morning. The hospital listed Vanchiro’s condition as critical as of 11:45 p.m. Sunday.

Vanchiro, 38, who also went by the alias Jeffrey Gamblero, was gaining fame as an enthusiastic Nets season-ticket holder who wore colorful outfits to Barclays Center and often ended up on the Jumbotron while dancing up and down the aisles of the arena.

Evans said Vanchiro had been behaving erratically since being ejected from Madison Square Garden on Dec. 2, when the Nets faced the Knicks. Video taken from the stands showed Vanchiro, who lost the lower part of his left leg in an accident several years ago, being carried out of the arena by multiple security guards. In the videos, which were widely shared in the news media that night and in the following days, Vanchiro is missing his prosthetic left leg, which he said that he had removed during an exchange with the security guards.