The reason is that previously high-ranking officials within the club were involved in a match-fixing scandal ten years ago, between 2012-2014.
Osasuna will appeal the decision to the Court of Arbitration for Sport, Cas.
Uefa announces that Athletic Bilbao will get the place instead.
Additional penalties may come.
Osasuna, who finished seventh last season in La Liga, were preparing to play in Europe for the first time since 2007.