Midfielder Ben Reeves has withdrawn from Northern Ireland's squad and been replaced by Billy McKay.
Reeves is receiving treatment at his club, MK Dons, and has been ruled out of the forthcoming Euro 2016 qualifiers against the Faroe Islands and Hungary.
Stiker McKay, who recently joined Dundee United on loan from Wigan, has been added in his place.
Manager Michael O'Neill also has doubts over Nottingham Forest forward Jamie Ward (hamstring), who has yet to link up with the squad, but is more positive about Chris Brunt's chances after he was injured on West Brom duty.
O'Neill told BBC Northern Ireland: "Chris Brunt is working separately with the medical team but we're optimistic rather than pessimistic about his chances of being involved on Friday night (in the Faroes).
"Jamie Ward we've left at Forest for the time being, we'll basically asses that on a day by day basis but Jamie, realistically, has the least chance of making it.
"Ben Reeves unfortunately has withdrawn and we've added Billy McKay."
Northern Ireland have defied expectations to sit second in Group F heading into the next round of matches.