Sepp Blatter says he will not stand down as Fifa president because of the criminal proceedings opened against him by Swiss investigators.
The Swiss, 79, is suspected of signing a contract that was "unfavourable to Fifa" and making a "disloyal payment" to Uefa president Michel Platini.
Blatter, who had already said he will stand down in February 2016, claimed he "had done nothing illegal or improper".
Platini, 60, has written a letter to Uefa members denying any wrongdoing.
In a statement released through his lawyers, Blatter said a £1.5m payment made to Platini, the head of European football's governing body, in 2011 was "valid compensation and nothing more".
Both men are also facing investigation by Fifa's independent ethics committee over the payment, which Platini said was for work as Blatter's technical advisor between 1999 and 2002.
Platini, who was interviewed as a witness by officers from the Swiss attorney general's office, stressed that the payment had been "fully declared" to the authorities.
The Frenchman said he was "aware that these events may harm my image and reputation" and released a statement for "reasons of transparency".
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The 2011 payment came nine years after Platini's work for Blatter - and two months before Uefa gave its backing to the Swiss before a presidential election.
That is something that now must be explained, according to Scottish FA chief executive Stewart Regan.
"It is an essential piece of information that still needs to be provided," Regan said.
The contract - described by Swiss prosecutors as "unfavourable to Fifa" - is thought to refer to a 2005 TV rights deal between Fifa and Jack Warner, the former president of Concacaf, the governing body of football in North and Central America and the Caribbean.
According to an investigation by Swiss broadcaster SRF in September, the deal allegedly resulted in a multi-million pound profit for Warner's company.
World governing body Fifa, which has been hit by several corruption allegations in recent years, has said it is co-operating with the investigation into Blatter.
Former Brazil legend Zico, who intends to stand in February's presidential election, called on Fifa's ethics committee to "act with great transparency" in an open letter to the organisation.
"It must disclose all its procedures so that reforms and Fifa elections are not contaminated by suspicions of corruption," he wrote.
Earlier this year the United States indicted 14 current and former Fifa officials and associates on charges of "rampant, systemic, and deep-rooted" corruption following a major inquiry by the Federal Bureau of Investigation.
Meanwhile, a separate Swiss investigation is looking into the bidding process for the 2018 and 2022 World Cups, which will be held in Russia and Qatar respectively.