The representatives of Cristiano Ronaldo and Jose Mourinho were warned that the structure of the their tax affairs was potentially risky, according to media reports in Spain.
An investigation sparked by a leak of more than 18 million documents has reported that Real Madrid star Ronaldo has routed at least €150 million in income through the British Virgin Islands tax haven since 2009, and that the Spanish tax authorities have been investigating his affairs for 12 months already.
The same reports say that current Manchester United manager Mourinho allegedly moved some of his income via six countries and a New Zealand based trust in his wife's name in a bid to minimise the taxes he would pay when he was Real Madrid coach between 2010 and 2013.
Government officials in England and Spain have called for Mourinho's tax bill to be re-examined with Mourinho's advisers alleged to have misled investigators while hiding money in a Caribbean tax haven. Mourinho has insisted he has "nothing to hide."
#Exclusiva �� Un bufete en las Islas Vírgenes proporciona la dirección a los clientes de Mendes https://t.co/H6u2vtowPR #FootballLeaks pic.twitter.com/CjHT3YNQvh
- EL MUNDO (@elmundoes) December 5, 2016
Both are represented by Jorge Mendes' agency Gestifute, which has strongly denied any wrongdoing, saying that all of their clients are fully compliant with all of their tax obligations.
However, an email printed by El Mundo allegedly shows that Madrid-based lawyers Senn Ferrero wrote to Gestifute to say that his opinion was that the combination of offshore companies created to manage Ronaldo's finances could come under scrutiny.
"The structure you have created gentlemen is going to cause a serious problem for the player [Ronaldo]," the leaked email allegedly written by Julio Senn, who was managing director of Real Madrid in the late 1990s and is now a leading sports law expert in Spain, read.
The publication of the leaked documents has caused a furore in Spain, especially with many details being printed on the morning of Saturday's 1-1 Clasico draw between Madrid and Barcelona at the Camp Nou.
On Monday, the union of Spain's tax agency employees called upon the agency to recommend that a criminal case for Ronaldo's taxes during 2011-13 be opened. They estimated that if Ronaldo were to be found in arrears, his fine could be as much as €600,000 for each of the three years. The union employees also said that if Ronaldo were to be found to have used tax havens, he could face a sentence of two to six years imprisonment.
Veteran radio host Jose Ramon de la Morena, a household name in Spain after three decades on late-night sports shows, was critical of rich individuals using complicated structures to hide earnings on his current programme El Transistor.
"The tax structure was created to steal from society," De la Morena said. "The taxes seem a lot to you if you earn a lot, and even more if you earn less, but these are rules set by the governments the people have chosen. This is the law.
"Before the guy who avoided taxes was the smart one, but now it is a crime where everyone feels they are the victim, as we are all being robbed. Everyone tries to do what they can, within the law. But to hide money to avoid paying taxes is to steal."
Among the leaked documents is correspondence between the father of Madrid starlet Martin Odegaard and the Senn Ferrero office, in which Hans Erik Odegaard declined to use any scheme which would have helped his son pay less tax
"[Martin] is going to earn a lot of money anyway," Odegaard Sr. is quoted as saying by El Mundo. "So there is also a moral question involved over how much effort should be made to try and save some money, when other people are struggling much more to pay their taxes."
Former Real Madrid player Mesut Ozil, now at Arsenal, paid more than €2m (£1.67m) in back tax in Spain and is disputing a €790,000 fine, according to documents supplied to Der Spiegel by Football Leaks.
It has also been reported by The Times that Mario Balotelli was entitled to a bonus payment of £1 million from Liverpool if he was not sent off on three occasions each season for violent conduct.