Michael ONeill has released Ciaron Brown and Shayne Lavery to allow the pair to Perform to the U21s in Romania.
Linfield striker Lavery and Cardiff shield Brown were in the 23-man senior team that travelled to Prague on Saturday before the friendly night.
But they have flown to Romania to join Ian Baracloughs squad at Voluntari on Monday night.
Baracloughs side endured a late defeat to Denmark in Aalborg on Thursday, leaving them after draws with Malta and Finland.
Lavery and Brown both showcased in the months friendly against Luxembourga game Brown began on his international debut.
Both players were in the framework to feature in Prague using ONeill place to provide use a number of players in his group following Thursdays heartbreaking defeat to Holland that left hopes of qualifying for Euro 2020 hanging by a thread.
No replacements will likely be called up departing 21 players for Monday to ONeill.