Deportivo La Coruna have been ordered to allow the transfer of Angel Lafita to Real Zaragoza.
Zaragoza exercised a buy-back option just before the transfer deadline at the end of last month but the move was held up by a dispute over finances.
Deportivo had argued the deal should not go through because their Primera Liga rivals did not pay their stated fee of 3.5million euros (£3.1million) plus sales tax.
Zaragoza insist the £2million euros they deposited with the Spanish football league (LFP) was the amount agreed in the contract between the two clubs.
The LFP has now ruled in Zaragoza's favour but Depor are still not happy and are expected to appeal the decision.
"The league have not answered the real question, which is the financial one," Depor president Augusto Cesar Lendoiro told his club's official website.
"It can be taken for granted he is a Zaragoza player, but what is being disputed is the cost of the move."