Police say the 33-year-old man, from the Bronx, was stabbed inside Columbus 72 on Columbus Avenue and West 72nd Street just before 3 a.m.
Patrons said they heard a popping noise, and then people started scattering. At that point, no one was quite sure what happened.
The victim was rushed to St. Luke's Hospital in critical condition, possibly with a gash to a major artery in his neck caused by a broken bottle.
The stabbing followed a reported dispute inside the club near the DJ booth.
Investigators were searching the scene for evidence and were reviewing surveillance video.
No arrests have been made, and the motive for the stabbing remains unclear.
The club had been hosting a Thursday night event. Residents say the club is frequently noisy on the weekends.