A 42-year-old man was sucker-punched in an unprovoked attack inside a Brooklyn subway station last Wednesday, police said.

Video of the assault provided by police shows the victim getting walloped in the face by an unidentified man in the Atlantic Avenue-Barclays Center subway station.

The victim was speaking on his cellphone when the suspect approached from behind and slugged him in the face, the video shows.

The two then briefly scuffled, making their way down the stairs, before the suspect could be seen heading back up and fleeing.

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The victim suffered cuts to his right cheek and above his eye. He was taken to Cobble Hill Hospital in stable condition, police said.

His attacker was still at large as of early Friday, according to police.

This story first appeared in the New York Post.