The victim was attacked near Broadway and Thornton Street in East Williamsburg around 7 p.m.
Police say the man in his 20s suffered two stab wounds to his back.
Paramedics rushed him to Bellevue Hospital in critical condition.
Witnesses say they saw a group of people running from the scene.
So far, no arrests have been made.
There is no word on a motive or what events led up to the stabbing.
