The Royals designated Selby for assignment Saturday.
Selby will lose his spot on the Royals' 40-man roster in order to make room for Kris Bubic (elbow), who was reinstated from the 60-day injured list Saturday. Selby hasn't pitched in the majors since early May, and he has posted a 6.23 ERA alongside a 1.18 WHIP over 21.2 frames with Omaha.