The former Sporting star spent the second half of the campaign with the London club after falling out of favour with Biscione boss Luciano Spalletti.
Mario’s disappointing play forced him to the bench, however he impressed while with the Hammers, and Calcio News 24 reports the English side are expected to exercise their €30 million option to make the move permanent.
Another player expected to depart the Giuseppe Meazza is Santon, who has endured another inconsistent campaign.
Watford have reportedly inquired about his services, though it appears Fiorentina and Sampdoria are in the mix to land his services.
The Viola appear to be the favourites to land the Nerazzurri youth product, who’s contract with the club expires in 2019.