Mario, a winner at Euro 2016 with Portugal, has started just five Serie A matches this term, but West Ham United is willing to pay his wages in full and hand over a loan fee to acquire his services on a temporary basis, according to the Guardian's Jacob Steinberg.
The Irons' need to strengthen their midfield was heightened when Manuel Lanzini suffered a ruptured hamstring during Saturday's 1-1 home draw with Bournemouth. The Argentinian is expected to miss around six weeks. The position was already an issue, with Moyes' predecessor, Slaven Bilic, publicly reprimanded by co-owner David Sullivan for passing off opportunities to sign Renato Sanches and Grzegorz Krychowiak before the summer window closed.
It's not just Lanzini in West Ham's treatment room. Marko Arnautovic is dealing with his own hamstring complaint, while Andy Carroll and Michail Antonio are long-term absentees. Defenders Jose Fonte and Winston Reid may be available for selection next week.
Mario, 25, is viewed as a player who can fulfill a few different roles in what's commonly a five-man midfield deployed by Moyes. The Scottish manager is reportedly also considering Real Betis' Fabian to bulk up the middle, a 21-year-old Spaniard who's tallied two goals and three assists over 16 La Liga outings this term.
Regular starters in the centre of West Ham's midfield include Pedro Obiang, Cheikhou Kouyate, and Mark Noble, while youngsters Declan Rice and Josh Cullen have submitted convincing cases for more first-team minutes.