Northern Ireland manager Michael O'Neill says Kyle Lafferty cited an Achilles injury when he withdrew from the squad for the Nations League games against Austria and Bosnia-Herzegovina.
The Northern Ireland boss said on Tuesday night that the Rangers striker had "ruled himself out" of the games.
O'Neill was informed of Lafferty's withdrawal on Sunday evening.
"Kyle had an Achilles problem, we knew he had an Achilles problem in September," said O'Neill in Vienna.
"He felt that it was in his best interests that he didn't travel because it gives him the opportunity to stay off the Achilles and that's the reason for him withdrawing from the squad."
Northern Ireland face Austria in Vienna on Friday evening before taking on the Bosnians in Sarajevo on Monday.
Given the importance of the next two games, O'Neill is keen to make sure Lafferty's absence does not become a distraction.
"I plan to have a chat (with him) but not before the game," added the Northern Ireland boss.
"The focus has been, really since the conversation, preparing the team to play. There's not another international after this until November so there's plenty of time to have that conversation.
"At the end of the day the player has made himself unavailable so we'll focus on the squad we have here."