A Manhattan pedestrian was slashed with a box cutter in an unprovoked attack, cops say. 

The assailant approached the 36-year-old male victim on Union Square West near East 15th Street around 9:40 a.m. Monday, police said. 

The stranger slashed the unsuspecting man in the back before fleeing into a nearby train station, authorities said. The suspect didn’t say a word during the assault.

The victim was taken to Bellevue Hospital, where he was listed in stable condition. 

The suspect — shown in a photo released by the NYPD on Monday night — had not been caught by Tuesday morning.