Arsenal boss Arsene Wenger believes introducing a quota-based system to the Premier League would be counter-productive.
Rangers boss Stuart McCall says he feels sorry for Gael Bigirimana, but admits he should never have been signed.
The 17-year-old will remain with his current club next season before making the move to England.
Milinkovic made six appearances for Serbia in the qualifying phase for the UEFA Under-17 Championship, keeping three clean sheets, but they just missed out on reaching the tournament.
He would follow in the footsteps of compatriots Nemanja Vidic and Zoran Tosic if he makes his way into the United first-team in the coming years.
The deal kicks off United's transfer business for the summer, although they remain without a permanent manager in the wake of David Moyes' dismissal last month - reports suggest Louis Van Gaal will be appointed early next week.