Real Madrid along with six other Spanish clubs are being investigated by the European Commission for receiving financial benefits from the state, according to the Sunday Mirror.
If found guilty they could be forced to pay back some of the money meaning the likes of Cristiano Ronaldo and Gareth Bale, purchased for world record fees, could find their Madrid futures in doubt.
Fellow giants and rivals Barcelona are also being investigated along with Valencia, Athletico Bilbao, Osasuna, Elche and Hercules.
However, the mass outlay of 'Los Blancos' puts them under most pressure, should they be found guilty of distorting competition.
The investigation includes allegations of earning money in the face of cheaper tax rates, cheap loans and cheap land deals with the local or central government.
Complaints from rival clubs such as Tottenham Hotspur, the club who sold Bale, and Borussia Dortmund have apparently started the investigation.
However, the Spanish government have denied the claims and will assist the clubs with any investigations.
The Spanish giants top the Deloitte money league after they became the first club to surpass £420 million in annual revenue, despite reported debts of around £500 million.
Bale and Ronaldo's transfer fee's combined stand at around £170 million. Their large outlay this season is intended to win a first Champions League title since 2002 and reestablish dominance over Barcelona who have had the upper hand over the last few years.
So far Carlo Ancelotti's men have safely reached the last-16 in Europe, but are in third place of La Liga.