Northern Ireland duo Craig Cathcart and Warren Feeney will miss Wednesday's friendly against Norway due to injury.
Cathcart and Feeney had been named in Michael O'Neill's original 24-man squad, but have been forced to withdraw from the new coach's first match.
Blackpool defender Cathcart had been in contention to start against Norway at Windsor Park, but has pulled out due to a hamstring complaint after missing his club's 3-1 win at Bristol City on Saturday.
Plymouth Argyle striker Warren Feeney has not featured in his side's last five games and will sit out the international friendly due to a calf injury.
No replacements have yet been named but, with the Under 21 side not in action this week, O'Neill has several options should he wish to strengthen his squad.