McKeown has not featured since early March because of a knee injury, and his season looks over following corrective surgery.
Killie will try and rally after missing out on a top six place because Dundee United scored in the final seconds of their game with Aberdeen in the last round of league matches.
Hearts boss Gary Locke is boosted by the availability of two of his experienced defenders when they travel to Rugby Park.
Andy Webster and Darren Barr were both fitness doubts for the game, but they have been passed fit.
Gordon Smith will face a late fitness test after he was injured midweek but Marius Zaliukas and Danny Grainger remain unavailable.