Nasser al-Khelaifi, the president of Paris Saint-Germain, appears to have sought payments for an agent which could have violated transfer regulations, and to have given inaccurate information to a French judge, according to leaked documents.

Khelaifi appears to have signed a letter to the chief of staff to the future emir of Qatar asking for a €2m payment to be made to Javier Pastore’s agent – when the Argentinian midfielder was transferred from the Italian club Palermo to PSG in a deal worth €40m plus bonuses in 2011. Another $200,000 in “expenses” was also requested for a private Qatari company, Oryx QSI, run by his brother.

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It is forbidden for a club president to personally pay an agent. According to article seven of Fifa’s regulations for intermediaries “any payment for the services of an intermediary shall be made exclusively by the client of the intermediary to the intermediary”.

The French Football Federation (FFF) confirmed to the Guardian and the French website Mediapart that such a payment would violate its regulations. The French Professional Football League (LFP) said it would also breach L. 222-17 of the Sports Code, which stipulates that only players and clubs are allowed to pay an agent. “A club president therefore can not, personally, directly fulfil the payment of commission to an agent,” it added in a statement.

The confidential letter, written in Arabic, also suggests that Khelaifi gave inaccurate information to Renaud Van Ruymbeke, a French judge who is an investigative magistrate, when he told him he did not have authority to sign. He told the judge: “I did not have the signature – I could not order any expense” for Oryx QSI in 2011. However, the letter was written on Oryx QSI notepaper and signed by Nasser.

The letter is included as an PDF sent by email in a large tranche of documents seen by the Guardian and Mediapart. Information in the letter has been supplemented by documents from Football Leaks, obtained by the German news magazine Der Spiegel.

It appears to describe an operation ordered by the current emir of Qatar, which aims to pay – through Khelaifi and the company Oryx QSI – an undisclosed commission to an agent.

The letter, apparently from Khelaifi, is addressed to “His Excellency Sheikh Khalid bin Khalifa Al Thani, Chief of Staff of His Highness the Crown Prince”, and includes the subject line: “Commission of the agent in charge of the player Javier Pastore and expenses of the company Oryx QSI.”

In the letter Khelaifi writes that his letter is “based on verbal instructions given by His Highness Sheikh Tamim bin Hamad Al Thani, heir to the throne, may God protect and conserve him, regarding the payment of the commission due to the agent in charge of the player Javier Pastore amounting to 2 million euros (2,000,000) in exchange for his transfer from the Italian club of Palermo to Paris Saint Germain, in addition to the expenses of Oryx QSI, amounting to US $200,000 (two hundred thousand US dollars).”

Details of where to make the payments are then given, before Khelaifi adds: “We thank you for your help and cooperation with us. Please accept, Your Excellency, the expression of my respect.”

Sheikh Tamim bin Hamad Al Thani succeeded his father as emir of Qatar in 2013.

When contacted by the Guardian with detailed questions, Khelaifi’s lawyers initially responded by saying that the states leading the blockade of Qatar – which includes Saudi Arabia, UAE and their allies – had circulated “a huge amount of misleading information and fabricated documentation purportedly referring to the State of Qatar and the activities of various of its citizens”.

They added: “In these circumstances … our client cannot admit either the authenticity of the material you have described but refused to provide … or the various conclusions you seek to draw from this.”

The Guardian and Mediapart offered precise information allowing Khelaifi to find the email regarding Pastore in his mailbox, as well as an English translation of the typed letter in the attachment.

On Monday evening, after publication of this story, lawyers for Khelaifi said that the document had been forged. “Our client will be filing a criminal complaint for forgery and use of forgery in France.”

Representatives for both Thanis refused to comment.

Facebook Twitter Pinterest Javier Pastore played for PSG from 2011 to 2018. Photograph: John Berry/Getty Images

Khelaifi has received a preliminary charge of “active corruption” as part of an inquiry into the bidding process for the 2017 and 2019 World Athletics Championships. During the bid a payment of $3.5m payment was made from Oryx to the marketing executive Papa Massata Diack which the French authorities suspect was a bribe.

Pastore’s agent Marcelo Simonian said he “didn’t know” the company Oryx QSI and that he did not negotiate the transfer of Pastore with Khelaifi. “With Nasser, we speak, we shake hands,” he added. “But the negotiation was done by phone with Leonardo [the sporting director of PSG].”

Simonian held 50% of the player’s economic rights under third-party ownership and was therefore entitled to half of the €40m transfer fee excluding bonuses – although he is still in dispute with Palermo over the payment.

The Argentinian was also representing Palermo in the deal although, under the French and international rules prohibiting an agent to represent several parties in the same operation, he was not allowed to be paid by PSG for the transfer.

However, confidential documents from Football Leaks appear to show that on 15 September 2011, a month after the transfer, a colleague of Simonian contacted the French lawyer Emmanuel Moulin about the Pastore deal – and asked him to get in touch with PSG to claim an amount which the club owed to Simonian. Football Leaks documents also suggest that Simonian was informed of this request.

According to those documents, an employee of Moulin’s law firm contacted Simonian and his acquaintance the next day, to tell them that Moulin had been in touch with PSG and that the club had confirmed that the payment was made. There was no indication of the sum involved.

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Presented with this information, Simonian any denied any wrongdoing. “Maybe you have misread or badly translated,” he replied. He said he did “not remember” such an exchange, adding that he “never asked PSG to be paid” regarding the transfer of Pastore.

“Neither me nor Emmanuel Moulin have received any commission on the transfer of Pastore. Zero,” he added. “I could not receive a commission because I was the co-owner of the player.”

Moulin declined to comment on the request for payment to PSG. But he rejected “with the utmost vigour” that there had been any wrongdoing or compliance issues regarding Pastore’s transfer or in the way it was reported to French football authorities.

• This article was amended on 15 July after a further response from Khelaifi’s lawyers.