A 53-year-old man had his throat slashed after getting into a beef with a second man outside a Brooklyn gym late Monday morning — with the accused slasher still on the loose, police said.

The violence erupted at Chelsea Piers Fitness gym on Schermerhorn Street around 10:45 am, when the victim and the assailant got into a dispute, an NYPD spokesperson said.

The attacker then came up behind the victim and cut his neck before fleeing, police said.

Images from the scene, which was cordoned off by police, show a puddle of blood on the sidewalk.

The victim, who was not identified, was taken to New York Presbyterian Brooklyn Methodist Hospital, where he was listed in stable condition, police said.

Cops said there have been no arrests in the assault and the investigation is ongoing.