Amad (Ivory Coast), Noussair Mazraoui (Morocco) and Bryan Mbeumo (Cameroon) have been called up by their respective nations for the tournament, which starts on Sunday 21 December.
The mandatory release date for clubs to release their African internationals is Monday 15 December, the same day that United are set to face Bournemouth at Old Trafford (20:00 GMT).
At the press conference to preview that match, which took place at Carrington on Friday, Amorim explained that there is a chance the players may be able to take part.
"We are still in conversation with national teams," began Amorim.