Koumas was dismissed for a second bookable offence as Mark Hughes' side held out for a 1-1 draw with the Finns.
Simon Davis gave the Welsh an early lead but striker Mikael Forssell, on loan at neighbours Birmingham City from Chelsea, levelled matter for the Finns with ten minutes remaining at the Millenium Stadium, Cardiff.
Albion's other Wales international Andy Johnson played for the last fifteen minutes of the game.