The leaks, which surfaced last week, centre on a system of tax avoidance set up by Ronald’s agent Jorge Mendes, via his company Gestifute.
The agency allegedly hid €185m (£154m, $197m) from tax authorities through a network of offshore accounts and companies in Ireland, the British Virgin Islands, Panama and Switzerland.
Real Madrid star Ronaldo and Manchester United manager Mourinho allegedly moved large sums to the British Virgin Islands.
Both Ronaldo and Mourinho have denied the claims, with Gestifute adding in a statement: “Any insinuation or accusation made to Cristiano Ronaldo or Jose Mourinho over the commission of a tax offence will be reported to the legal authorities and prosecuted.”
A group of 12 European newspapers said it intends to disclose over the next three weeks the results of investigations, based on 18 million documents of leaked data, into widespread alleged corruption at the heart of football under the banner “Football Leaks”.
The documents claim to show that Ronaldo could have “hidden €150m euros in tax havens in Switzerland and the British Virgin Islands”.
One of the papers in the European Investigative Collaborations (EIC) consortium, the Dutch NRC, alleges that Ronaldo moved €63.5m to the British Virgin Islands at the end of 2014.
The striker received sponsorship fees which were moved via two Irish companies to the offshore jurisdictions, 11 days before Spain changed an advantageous tax law, said the publication.
Meanwhile, the EIC claims that Mourinho moved €12m into a Swiss account owned by a British Virgin Islands company.
The leaked documents relate to the time that Mourinho spent as manager of Real Madrid, between 2010, and 2013, reported Spanish newspaper El Mundo.
Spain, football and tax avoidance
The revelations come as an increasing number of football players have fallen foul of Spanish tax authorities in recent years, including Barcelona stars Neymar and Lionel Messi.
In July, Argentinean footballer Messi and his father were sentenced to 21 months in prison by a Spanish court for tax fraud over €4.1m the pair squirrelled away in tax havens in Belize and Uruguay between 2007 and 2009.
Neymar and his father are also facing a two-year prison sentence and a $10.6m fine on corruption charges related to alleged irregularities during his transfer from Brazilian club Santos to Barcelona in 2013. They have denied wrongdoing.