The Polish player was driving through the Varcaturo district at around 2 a.m. when the motorbike blocked the road and forced him to stop, the report said.
One of the men pointed a gun at Milik and made him hand over a Rolex watch. Naples police could not immediately be reached for comment.
Two years ago, Napoli forward Lorenzo Insigne, who scored the last-minute winner on Wednesday, and his wife were mugged in the city in similar circumstances. Media reports said the robbers told Insigne to "score a goal for us" in his next match.
Team captain Marek Hamsik was robbed in 2013 as was his wife two years before that.
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(Writing by Brian Homewood; Editing by John O'Brien)
