These four have been identified as 'Red Devils' targets for the January transfer window, but whether or not Manchester United have the funds to bring in these players depends on if the board back the Portuguese.
Mourinho had targeted Perisic and Rebic in the summer, though the board did not allow him the funds to bring them in.
The same goes for Serbian duo Milinkovic-Savic and Milenkovic, who the Portuguese admires.
As reported by 'Sportsmail', more than ten players could see their contracts expire at United this summer, so if Mourinho can bring in either of these four players they will add strength to an under-performing squad.
The 'Red Devils' boss watched over Serbia's Nations League win over Montenegro on Thursday, reportedly keeping a close eye on the Serbian duo, who were both involved.