Aberdeen winger Niall McGinn is heading for a scan on the injured ankle that forced him to withdraw from the Northern Ireland squad to face Finland.
The 25-year-old is on crutches after being stretchered off during Saturday's 0-0 draw with Ross County.
McGinn's scan will determine whether the summer signing suffered ligament damage, but he is likely to be sidelined for at least a month.
He fell awkwardly in a challenge with County defender Grant Munro.
Brown blows hard in the dugout after losing one of his two summer signings through injury
McGinn had been called up after being omitted from Northern Ireland manager Michael O'Neill's original 23-man squad.
But he has now withdrawn through injury for Wednesday's friendly along with Celtic winger Paddy McCourt, Fulham defender Aaron Hughes and Liverpool midfielder Ryan McLaughlin.
Aberdeen manager Craig Brown had said immediately after Saturday's game at Pittodrie: "Niall was included in the squad for midweek, but he won't have any chance of going there because he has twisted his ankle.
"We can't tell the length of the recovery period."
Brown said that McGinn, who had been signed after leaving Celtic, had been looking forward to the international at Windsor Park.
"I thought it was a head knock at first because he was holding his head, but I think that was just out of his disappointment, not only from the point of view his club Aberdeen but also the Northern Irish team," said the manager.
McGinn was not the only disappointed player in the home dressing-room after the 0-0 draw with the Scottish Premier League newcomers.
"The lads are in there apologising for the misses," said Brown. "Gavin Rae is distraught and Scott Vernon is the same.
"Anyone who's fair-minded and independent would agree that we dominated the game.
"We created enough chances to win several games but didn't convert them.
"We did play well in the match. We were not under any pressure at all, but give them credit, they came for a point and got a point.
"I thought Stephen Hughes was immense in the game, but for now we are a little despondent as we did not get the win."