The six-times capped Sweden international only moved to Vicarage Road
last summer from Ostersunds FK and made 22 appearances for the English
The 25-year-old's departure follows the arrival of Senegal
international Ismaila Sarr to the Premier League outfit on a club record
transfer of €35 million from Rennes.
The north-eastern Italian club and Watford are both owned by the Pozzo family.
Udinese host AC Milan in their opening match of the Serie A season on Saturday.