Real Madrid launched a staunch defence of star forward Cristiano Ronaldo on Tuesday, demanding respect for the three-time World Player of the Year amid allegations he hid millions of euros earned from image rights in tax havens.

"Real Madrid demand the maximum respect for a player like Cristiano Ronaldo, whose behaviour has been exemplary during his entire time at our club," Madrid said in a statement.

An international consortium of media organisations on Friday claimed that a huge data leak involving 18 million documents showed the Portuguese skipper hid 150 million euros ($160 million) from image rights in the British Virgin Islands.

Ronaldo, 31, has strongly denied the claims in a statement via Gestifute, the firm controlled by his agent Jorge Mendes.

"Cristiano Ronaldo has always acted in good faith in this matter, as the fact that he has never been involved in any conflict with the Tax Authorities from any country where he has lived clearly shows," said Gestifute.

Gestifute also released a tax return issued by the Spanish tax agency showing Ronald is up to date with his obligations.

"The certificate released by the Spanish tax agency which shows our player Cristiano Ronaldo is up to date with all his tax obligations," added the Madrid statement.

Madrid destabilised

Ronaldo is just one of a series of Madrid players to have been accused by the "Football Leaks" investigation into corruption in football.

Spanish newspaper El Mundo accused Portuguese defenders Pepe and Fabio Coentrao, also both clients of Mendes, of selling their image rights to companies in the British Virgin Islands and Panama respectively.

Pepe was reported to have earned 3.7 million euros in image rights since signing for Madrid in 2007 and Coentrao 3.5 million since 2011.

"Given the information published in the media, I inform that I am up to date with my tax obligations," Pepe said in a statement released on his Instagram page on Tuesday.

"In previous years I voluntarily and anticipating any requirement on behalf of the tax agency came forward to regulate my income from image rights given the change of criteria used by the Spanish tax office."

Croatian midfielder Luka Modric was also accused by El Mundo on Tuesday of diverting income derived from his image rights to a company registered in Luxembourg.

Ahead of Real's crucial Champions League clash with Borussia Dortmund on Wednesday, captain Sergio Ramos claimed some of the accusation were designed to destabilise the European champions.

Madrid are on a 33-game unbeaten run stretching back to April.

"Some of it will be true, others designed to destabilise the group when we are in great form," said Ramos.

"I don't think it will have any special importance on the group."