Subject to global clearance, the Portugal Under-21 worldwide will embark on his fifth spell away from Old Trafford.
A Portugal U21 global, he has been loaned to Belenenses and Vitoria Setubal and spent the second half of last season at Kortrijk in Belgium. Despite his many loan moves, however, he is yet to make more than 10 appearances for a single side.
Pereira will be available for Friday's League Cup visit to Motherwell if clearance arrives in time.
The keeper will provide competition for places with Hearts' first-team stoppers Zdenek Zlamal and Colin Doyle.