Marco Cassetti, Joel Ekstrand, Ikechi Anya, Daniel Pudil and Almen Abdi, all of whom spent last season on loan at Vicarage Road, are poised to sign for the Championship club on a permanent basis.
Udinese trio Gabriele Angella, Marco Davide Faraoni and Jaime Romero have also been targeted by Gianfranco Zola's side, who are currently on a pre-season tour of Italy.
Faraoni's agent, Giovanni Bia, confirmed earlier this week that a move to Watford was an option for the defender.
"We are talking about and evaluating the prospect of him going to Watford," Bia said.
"If the guy leaves Udine he will almost certainly go there because it is a club with links to Udinese and we believe it would be the best solution for everyone.
"We would like to make a decision soon. Faraoni is in a hurry to know his future."
Watford, who were beaten in last season's Championship play-off final, took advantage of a loophole in regulations last season by making 14 loan signings from abroad.
However, Football League clubs voted unanimously in favour of limiting the number of overseas loan players in matchday squads to five, and a maximum of eight players brought in on loan throughout the course of a season.