Since arriving at Vicarage Road, head coach Marco Silva has added Daniel Bachmann, Kiko Femenia and Will Hughes to his first-team squad, but it appears that he is planning more changes at his new side.
According to Sky Italia, Strinic and Defrel will both have the opportunity to sign for the Hornets during the summer transfer window.
Left-back Strinic has been limited to just 39 appearances in three years in Naples and although he has the option of penning a new deal, he is expected to move on this summer.
Defrel has been linked with Liverpool, West Ham United, Southampton and Roma since the end of last season after netting a total of 14 goals in Serie A and the Europa League.
However, with more first-team opportunities potentially available at Watford, he has emerged as a serious target for Silva.