The Sweden international has struggled for minutes this season with the Hornets.
Sky Italia's Gianluca di Marzio reports he could now return to sister club Udinese on-loan to the end of the season.
Sema spent the 2019/20 season on-loan with the Zebrette.
Watford and Udinese are owned by the Pozzo family and it is not uncommon for players to move between clubs.
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