Koumas, 27, suffered a foot injury in the 2-0 defeat to Germany in Cardiff on Saturday, and will not be able to train for the next two days.
Wales boss John Toshack sent Koumas back to Wigan for treatment on Monday as the squad prepared to fly out from Cardiff.
Copyright (c) PA Sport 2007, All Rights Reserved.
Do YOU want to write for GiveMeSport? Get started today by signing-up and submitting an article HERE: https://www.givemesport.com/writeforgms