Fifa president Sepp Blatter's top deputy has denied allegations that he is the high-ranking official who made key payments in a bribery scandal engulfing world football.
The New York Times and other media named Jerome Valcke as the person responsible for a $10m (£6m) transfer of funds cited in a US indictment.
A letter has emerged apparently linking Mr Valcke to the payment.
But Fifa has strongly denied that Mr Valcke or other managers were involved.
Mr Valcke is not under indictment and prosecutors have not accused him of wrongdoing.
Last Wednesday, world football was rocked when seven senior Fifa officials were detained at an annual convention in Zurich, among 14 people indicted by US prosecutors.
Mr Blatter is not one of the accused. He went on to win re-election for a fifth term as Fifa president, extending his 16-year reign.
On Monday, Mr Valcke announced that he would not be attending the opening of the Women's World Cup in Canada on 6 June as planned - a move that correspondents called "highly unusual".
The claims about Mr Valcke concern a corruption case being investigated by US authorities - the alleged payment of bribes over South Africa's bid to host the 2010 World Cup.
Prosecutors allege that a $10m payment made by Fifa to accounts controlled by former Fifa vice president Jack Warner constituted a bribe to Mr Warner in exchange for his support for the South African bid.
The bribe was promised in 2004, as Fifa considered the bid, but in the years afterwards South Africa was unable to pay, the indictment says.
So in 2008 Fifa diverted funds that would have gone to South Africa in support of the tournament, and itself made the payment to a group controlled by Mr Warner. Mr Warner took much of that money, prosecutors say, for his personal use.
Unnamed US officials and well-placed sources told the New York Times, Wall St Journal and Reuters news agency that the unidentified "high-ranking official" alleged in paragraph 192 of the indictment to have "caused" the payments was Mr Valcke, Fifa's secretary general.
Mr Valcke is not named as a defendant and the indictment does not suggest the official knew the money was allegedly being used as a bribe.
A letter seen by the Press Association news agency's chief sports reporter, dated 4 March 2008, in which the president of the South African Football Association appears to request the diversion of funds, is addressed directly to Mr Valcke.
But a Fifa spokesperson told the BBC the letter was "nothing new" and it was standard practice for the organisation's secretary general to receive "all letters and requests to the administration".
Payment 'for a project'
In an email to the New York Times, Mr Valcke said he had not authorised the payment and had no power to do so.
A Fifa spokeswoman said the payment was authorised by the then-finance committee chairman, Julio Grondona, who died last year.
Fifa says the $10m payment went towards a legitimate "project to support the African diaspora in Caribbean countries as part of the World Cup legacy" - an account echoed by key South African officials.
"Neither the Secretary General Jerome Valcke nor any other member of Fifa's senior management were involved in the initiation, approval and implementation of the above project," the statement said.