Mazzarri has his second Serie A signing in as many days.
The Hornets issued a press release on Thursday afternoon officializing the transaction.
“Watford FC is pleased to confirm the capture of exciting young AC Milan forward M’Baye Niang.
The highly-rated 22-year-old has signed on loan until the end of the 2016/17 season, and the Hornets also have the option of making the move permanent in the summer.”
Niang had played in 18 matches with the Rossoneri, finding the back of the net on only three occasions.
Slide for more related news