An employee of a popular Brooklyn diner was knifed in front of his workplace early yesterday, authorities said.

The 41-year-old porter at Dizzy’s Diner on Ninth Street near Eighth Avenue in Park Slope was slashed on the arm, chest and back at 2:20 a.m., said cops.

The porter, whose name was not released, was rushed to Kings County Hospital, where he underwent surgery.

He was in stable condition yesterday, cops said.

Police described the assailant as a man in his 20s. No arrests have been made in the case and authorities aren’t sure what set off the violence.