Athletic Bilbao could be forced to pay Javi Martinez's former club Osasuna €800,000 following the midfielder's move to Bayern Munich.
Martinez, 23, joined Bayern for a Bundesliga record fee of €40 million in August, and Osasuna claim they are entitled to the money due to a clause in the deal that took the midfielder to the San Mames.
Athletic seem unwilling to part with the cash following the transfer, forcing Osasuna to appeal to FIFA for the money.
The Spain international came through the ranks of the team from Pamplona, but was signed by the Zurigorri in 2005 for €6 million when he was just 17 years old.
Due to an agreement between the clubs, Osasuna were expecting to receive a fee as part of the player's sell-on clause, but as Martinez bought out his contract, Athletic believe this invalidates this part of the deal.