Phish lead singer Trey Anastasio, on left, and bassist Mike Gordon perform on stage at Keyspan Park on Coney Island June 17, 2004 in Brooklyn, New York.
New York State Park Police say the man jumped from the top deck to a seating area about 25 feet below during Wednesday night's concert. He was then airlifted to Nassau University Medical Center. He was not identified.
A spokeswoman said Thursday the man was in critical, but stable, condition.
One spectator below reported a minor injury. Police didn't say whether the jumper will face charges.
At least two concertgoers said the injury took place during an intermission in the popular jam-band's performance.
The show continued after the intermission without incident.