Gareth Bale’s agent has called for an investigation after a confidential document relating to his client’s world record £85m move to Real Madrid from Tottenham was leaked.

The six-page document, released by the website Football Leaks and widely published in Spain, set out details of the full value of the deal, which has always been disputed.

Real have long claimed they paid €91m (£78m) for Bale in 2013 – less than the €96m they paid for Cristiano Ronaldo four years earlier. However, the Spanish newspaper AS reported that the document showed the Bale fee amounted to €100,759,418 (£85m) – because Real had opted to pay in instalments – with Tottenham forbidden from disclosing any financial details.

It is widely thought that Real’s insistence that Ronaldo was the more expensive of the two players was designed to appease the Portugal forward. Earlier this month the journalist Jonathan Northcroft told the BBC he was asked by Real not to mention the subject when he interviewed Bale, “because Cristiano Ronaldo doesn’t like to see that someone else cost more than him”.

In October 2013 the Real president, Florentino Pérez, implied that Ronaldo’s fee was higher. Asked by the Spanish TV show Punto Pelota on the channel Intereconomia whether Bale had been insured for €91m, he replied: “Yes, of course.”

Bale’s agent, Jonathan Barnett, called the reports “outrageous”, telling the Telegraph: “There should be an inquiry and an independent investigation … I think it’s disgraceful that people can get hold of this sort of stuff. It shows complete disregard for both clubs and the player.”