18.07 As a rule, a player may not play in a UEFA club competition (i.e. UEFA Champions League and UEFA Europa League, but not UEFA Super Cup) for more than one club in the course of the same season. Exceptionally, however, player who has been fielded in the first, second, third qualifying round or the play-offs of the UEFA Champions League or UEFA Europa League is entitled o play in the UEFA Champions League or UEFA Europa League for another club as from the group stage. Moreover, as from the start of the round of 16, a layer can be registered in accordance with paragraphs 18.18 to 18.21 below.
A substitute player who has not been fielded is entitled to play for another club competing in the UEFA Champions League or UEFA Europa League in the course of the same season, provided that he is registered with the UEFA administration in accordance with the present regulations.