The former France U21 international has followed Mauro Zarate in joining the Hornets, signing on loan from AC Milan until the end of the season
Watford have signed AC Milan forward M'Baye Niang on loan until the end of the season with a view to a permanent move.
The 22-year-old has made 18 appearances for Milan in Serie A this season, but, after seeing him score just three goals, the Italian club have opted to allow him to kick-start his career in the Premier League.
He has previously spent loan spells at Montpellier and Genoa during his career at San Siro.