Fifa is facing fresh embarrassment just six weeks after Gianni Infantino took over as president of world football's governing body and pledged to clean up the crisis-hit organisation.
A key member of its ethics committee, Uruguayan lawyer Juan Pedro Damiani, is being internally investigated for links with Eugenio Figueredo - an allegedly corrupt football official.
Damiani has acted in sensitive ethics cases involving leading football officials since July 2012.
Part of a huge tranche of leaked documents, seen by the BBC, suggest that Damiani and his firm provided legal assistance for at least seven offshore companies linked to Figueredo, a former Fifa vice-president who was arrested last May in Zurich as part of the US inquiry into football corruption.
Figueredo was charged by US authorities with wire fraud and money laundering for his role in the alleged bribery conspiracy.
Despite that, he was extradited to Uruguay in December where he was also wanted on similar charges.
Discovery of his links to Damiani are the result of a leak of over 11 million documents from the internal files of Mossack Fonseca, a Panama-based law firm that specialises in helping the wealthy and powerful set up offshore companies.
The documents were obtained by the German newspaper Suddeutsche Zeitung and shared with the International Consortium of Investigative Journalists (ICIJ).
BBC Panorama and The Guardian newspaper are among 107 media organisations in 78 countries which have been analysing the documents.
The records do not show illegal conduct by Damiani or his law firm but a spokesman for Fifa's ethics investigatory committee told the BBC in a statement: "We confirm that on 19 March the investigatory chamber of the independent ethics committee was informed by the chairman of the adjudicatory chamber, Hans-Joachim Eckert, about becoming recently aware of a business relationship between the member of the adjudicatory chamber Juan Pedro Damiani, and Eugenio Figueredo Aguerre.
"After receiving the information Dr Cornel Borbely, chairman of the investigatory chamber of the ethics committee, has immediately opened a preliminary investigation to review the allegations in question. Dr Borbely is currently looking into said allegations in order to determine if there is a breach against the Fifa code of ethics and decide any further measures."
Fifa president Infantino has spoken repeatedly of a "new era" for football after being elected as Sepp Blatter's successor in February.
The leaked documents linking Damiani to Figuredo are therefore likely to raise questions over the strength of Fifa's background checks into ethics committee members.
In addition, two other executives charged in connection with the US football corruption probe have links to Damiani's legal and accountancy firm.
Hugo Jinkis and his son Mariano are currently under house arrest in their native Argentina, fighting an extradition request to the US on corruption charges.
They are mentioned in correspondence between Mossack Fonseca and Damiani's law firm regarding an offshore company they owned called Cross Trading.
Cross Trading was originally incorporated in 1998, on the Pacific island of Niue.
It then relocated to Nevada, USA in 2006 as Cross Trading LLC.
The leaked papers list Hugo Jinkis as a "beneficiary" of the company.
The records suggest that Damiani's law firm provided services for Cross Trading while it was in Niue as well as in Nevada.
According to the leaked documents Damiani and his law firm, JP Damiani & Asociados, have acted on behalf of hundreds of companies registered with Mossack Fonseca.
A spokesman for Damiani told the International Consortium of Investigative Journalists, prior to knowing he was under investigation, that he was not authorised to make statements while officials in Uruguay are investigating allegations of corruption related to Fifa.
He added that Damiani has taken a lead in reporting corrupt practices within Fifa to Uruguayan authorities and to Fifa's ethics committee.
Damiani has not responded to requests from the BBC to comment on the information contained in the leaked documents.
The extent to which Fifa officials and others connected to football have used offshore companies is also suggested in the huge leak of Mossack Fonseca documents.
Jerome Valcke, the secretary general of Fifa from 2007 until he was sacked by the governing body in January this year, also appears in the papers.
Valcke was banned by Fifa's ethics committee for 12 years in February for a series of breaches concerning its code of ethics.
Swiss authorities opened criminal proceedings against him earlier this month concerning "various acts of criminal mismanagement".
Panama Papers - tax havens of the rich and powerful exposed
- Eleven million documents held by the Panama-based law firm Mossack Fonseca have been passed to German newspaper Sueddeutsche Zeitung, which then shared them with the International Consortium of Investigative Journalists. BBC Panorama is among 107 media organisations - including UK newspaper the Guardian - in 76 countries which have been analysing the documents. The BBC doesn't know the identity of the source
- They show how the company has helped clients launder money, dodge sanctions and evade tax
- Mossack Fonseca says it has operated beyond reproach for 40 years and never been accused or charged with criminal wrong-doing
- Tricks of the trade: How assets are hidden and taxes evaded
- Panama Papers: Full coverage; follow reaction on Twitter using #PanamaPapers; in the BBC News app, follow the tag "Panama Papers"
- Watch Panorama on the BBC iPlayer (UK viewers only)
Documents suggest not only the extent of Valcke's wealth but also how he used Mossack Fonseca to create and then be installed as the hidden owner of a British Virgin Islands company called Umbelina SA.
Umbellina was used to purchase a 2.8m euro yacht, which Valcke subsequently renamed 'Ornella', after his current wife.
A source close to Valcke said the yacht was declared to the relevant tax authorities.
Furthermore it is claimed the company was not used for any other commercial or business purposes.
There is no suggestion of any wrongdoing by Valcke but the disclosure suggests the extent to which individuals within the football world use offshore companies to hide ownership of assets.
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