Hacienda, the Spanish Tax Office is looking into the deal that took Filipe Luis from Deportivo la Coruna to Atletico Madrid in July 2010.
The Brazilian left-back moved from Deportivo La Coruna to Atletico for a fee in the region of £9.5m, with Deportivo now complaining that they are still yet to recieve the full amount for the player.
The fee was supposed to be paid over a period of two years and reports in Spain suggest that authorities are now looking into whether Depor paid the right amount of VAT over that period.
And Chelsea could yet also be involved after it was revealed that Deportivo were set to receive a percentage of any future sales of the player.
By Ollie Brown