The defender had originally been included as one of the 22 players in contention to play in the friendly match at the Burgemeester Van de Wielestadion in Deinze next Thursday.
Falkirk are due to play Queen of the South two days before in a game that is a must-win if the club are to keep their promotion hopes alive.
Duffie has been in stunning form since taking over the right-back slot from Jason Marr at the turn of the year and has firmly established himself as a key component of Steven Pressley’s side.
As a result the Falkirk gaffer was reluctant to lose the services of the 19-year-old for the trip to Dumfries and his appeal was accepted by national coach Billy Stark.
Duffie made his debut for the under-21s in a 3-1 victory against Northern Ireland in November last year.
The Scotland under-21 squad are scheduled to travel to Belgium on the Monday.
However the Bairns are still likely to be represented in the match, with keeper Michael Andrews, currently on loan to East Stirling, and Ross Perry, on loan from Rangers both in the squad.