Brosuqe signed a new three year contract with the A-League side last July but it was not due to begin until April 1.

Today an independent arbitration tribunal found Brosque was therefore still playing under his old contract which didn't expire until the end of March and had a $400,000 buy out clause.

Shimizu have taken advantage of the clause to snatch Brosque from Sydney on the eve of their Asian Champions League campaign.

Now Sydney have threatened to take their fight to FIFA after claiming Shimizu approached Brosque about a transfer before they had cleared it with Sydney.

Tapping up is illegal under FIFA rules if a player has more than six months left on his contract. It is the grey area about his previous contract ending and the new on beginning which has caused Sydney the headache.

Today they begrudgingly allowed Brosque to leave the club - but have not ruled out further action.

"The arbitrator did not have the jurisdiction to hear arguments in relation to Shimizu S-Pulse's breach of article 18.3 of the FIFA Transfer Regulations," Vice-Chairman Scott Barlow said.

"Sydney FC will now consider its options as to filing a complaint with FIFA."

A club statement added: "Sydney FC considers itself to be an advocate for clubs, in particular A-League clubs, standing up for themselves and their beliefs and not bowing to the demands of cashed up clubs from around the world who've acted outside FIFA regulations.

"The club strongly believes it was right with the decisions it made and stands by them. For Sydney FC, it was always a matter of principle and acting professionally."

Barlow added: "Alex Brosque has been a great servant to Sydney FC. We wish him all of the best for the future and hope to welcome him back one day."

The striker is expected to fly out to Japan tomorrow.