The Daily Mail says the 27-year old was at Watford's training ground on Monday to complete his move.
The left-sided defender has agreed a three-and-a-half year contract with an option for a further year.
Samir, who has started 17 Serie A games this season, will be confirmed as a Watford player later this week.
Reports in Italy suggested that Udinese wanted defender Christian Kabasele to head in the opposite direction.
However the Watford Observer claims that the 30-year-old Belgian is not likely to be departing this month.
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