A man was slashed in the arm inside a Manhattan subway station on Monday before stumbling onto the tracks, cops said.

The suspect pulled a “cutting instrument” after he and the victim got into an argument while standing on a northbound F train platform inside the Second Avenue station around 5:30 p.m., cops said.

The victim stumbled onto the roadbed after he was slashed on the right arm, but was able to pull himself back up to safety, law enforcement sources told The Post.

He was rushed to Bellevue Hospital in critical condition, the NYPD said.

The assailant fled from the station. No arrest has been made.

The suspect was last seen wearing a gray shirt and black Adidas pants with white stripes, sources said.