Barcelona, Werder Bremen and Schalke had taken their case to CAS after arguing that FIFA's position that it was "mandatory" for all players aged 23 and under to be released was not enforceable as the Olympics do not appear on FIFA's official calendar.

The decision means that Barcelona will pull Lionel Messi out of the Argentina squad, while Brazil duo Rafinha and Diego will be recalled from by Schalke and Werder Bremen respectively.

It is not expected that any other players will be withdrawn as they have travelled with the permission of their clubs.

"The Court of Arbitration for Sport (CAS) has upheld the appeals filed by FC Schalke 04, SV Werder Bremen and FC Barcelona against the decision issued on 30 July 2008 by the Single Judge of the FIFA's Players' Status Committee that consequently has been set aside in its entirety," said a CAS statement.

CAS found that FIFA's position was based on custom rather than law, meaning clubs could not be forced to release their players.

The statement continued: "The Olympic Football Tournament Beijing 2008 is not included in the Co-ordinated Match Calendar and there is no specific decision of the FIFA Executive Committee establishing the obligation for the clubs to release players under 23 for this tournament.

"The requirements to justify a legal obligation of clubs to release their players for the Football Tournament Beijing 2008 on the basis of customary law are not met."

The three clubs made the appeal as they do not want the players to miss the start of the season. The Bundesliga season in Germany begins before the conclusion of the Olympics and Schalke will also play a Champions League qualifier.

Barcelona will have also have a Champions League qualifier to play before the Olympics conclude.