Barcelona striker Lionel Messi says he will defy his Spanish club's orders and join up with Argentina's Olympic squad this week.

The Argentina international has been at the centre of a tug of war between club and country with Barcelona trying to retain him for their Champions League qualifyier tie in August.

Messi, speaking before a FIFA judge declared that clubs were under an obligation to release their under-23 players for Beijing, said: 'If FIFA say I should be there then I'll go without waiting for CAS (Court of Arbitration for Sport) ruling.'

Barca have announced they will contest FIFA's ruling to CAS.

Messi added: 'If CAS say that I have to return then I'll come back but for the moment I want to be with my country and my teammates.'

The player has until Friday to link up with coach Sergio Batista's Argentina's Olympic squad in training in Japan.

Messi's stance was backed by the FIFA-appointed judge's ruling confirming clubs were obliged to release players aged 23 for the Olympics.

A statement issued by world football's governing body FIFA confirmed the judge of the Players' Status Committee, Slim Aloulou, agreed with FIFA's previous ruling that it was 'mandatory' for players to be released for Olympic duty.

The judge was called to rule on the matter after Werder Bremen, Schalke and Barcelona questioned FIFA's stance as the Olympics do not appear on FIFA's official calendar.

Bremen and Schalke are unhappy with the inclusions of Diego and Rafinha, respectively, in the Brazil squad.

CAS will now have the final say on the matter after Bremen, Schalke and Barca filed complaints.