The London club, who won last season’s FA Cup, fell foul of Uefa’s rules governing multi-club ownership.
European football’s governing body determined that as of March 1, American businessman John Textor had control or influence in Palace and French club Lyon.
It means under Uefa rules they are unable to compete in the same European competition and Lyon held on to the Europa League spot by virtue of their higher league position.
Palace appealed to Cas last month after Textor agreed to sell his 43 percent stake in the Premier League club to New York Jets owner Woody Johnson.
However, that deal was struck well after Uefa’s deadline of March 1 for multi-club conflicts to be resolved.
“After considering the evidence, the Panel found that John Textor, founder of Eagle Football Holdings, had shares in CPFC and OL and was a Board member with decisive influence over both clubs at the time of Uefa’s assessment date,” Cas said in a statement.
“The Panel considered that the Uefa Regulations are clear and do not provide flexibility to clubs that are non-compliant on the assessment date, as CPFC claimed,” it added.
Palace, who beat Liverpool on penalties to win the Community Shield after a 2-2 draw at Wembley on Sunday, will enter the Uefa Conference League in the play-off round later this month.
Nottingham Forest, who finished seventh in the Premier League, are set to replace Palace in the second-tier Europa League. (AFP)