Officials at Syosset Hospital called 911 at 9:45 p.m. to report they were treating a victim of a stabbing to Nassau County police.
But when police arrived, Gotti, the former boss of the Gambino crime family. was uncooperative and refused to assist police in their investigation.
Gotti transported himself to Syosset Hospital, and was then transferred to North Shore University Hospital for further treatment.
He has since been treated and released for his injuries.
"The Nassau County District Attorney's office can confirm they are investigating, in conjunction with Nassau County Police, an alleged stabbing of John "Junior" Gotti," a spokesman for the district attorney's office said.
Gotti said he was hurt while trying to break up an argument between two strangers in the store parking lot.
A law enforcement source tells ABC News that Gotti sustained a stomach injury.
Detectives are collecting security camera video from the scene.
Gotti says he quit the mob in 1999, claiming he'd had enough of being a gangster and wanted to focus on being a father.
