Swiss prosecutors have opened a criminal investigation into Sepp Blatter, the head of football's world governing body FIFA.
The attorney general's office said he was suspected of criminal mismanagement or misappropriation over a TV rights deal and of a "disloyal payment" to European football chief Michel Platini.
Mr Blatter was being questioned, and his office was searched, it added.
Fifa said it was co-operating with the investigation.
Mr Blatter, 79, has run FIFA since 1998 and has always denied any wrongdoing.
The Swiss attorney general's office said the investigation surrounds a TV rights deal Mr Blatter signed with former Caribbean football chief Jack Warner in 2005.
"Swiss criminal proceedings against the president of FIFA, Mr Joseph Blatter, have been opened... on suspicion of criminal mismanagement... and - alternatively - misappropriation," it said.
Mr Blatter is also suspected of making a "disloyal payment" of two million Swiss francs ($US2m) in 2011 to Michel Platini, the head of the European football body Uefa, the statement said.
It said the payment was "at the expense of FIFA, which was allegedly made for work performed between January 1999 and June 2002".
Mr Blatter is due to step down in February and Mr Platini is widely expected to replace him.
In May, Swiss authorities arrested seven FIFA officials in Zurich at the request of the US. They face extradition.
The US then unveiled indictments against seven other people in their corruption case, nine of whom are high-ranking officials.
Among them was Jack Warner, president of the Caribbean football association Concacaf and one of the most powerful men in world football.
He is currently in Trinidad awaiting extradition to the US on charges of corruption.
The Swiss opened their own investigation into FIFA hours after the initial arrests.
FIFA owns the TV rights to the World Cup and sells them to regional federations which then sell them on to broadcasters.
Mr Blatter's lawyer, Richard Cullen, said he was confident the inquiry would clear Mr Blatter of any wrongdoing regarding the contract with Jack Warner.
"We are confident that when the Swiss authorities have a chance to review the documents and the evidence, they will see that the contract was properly prepared and negotiated by the appropriate staff members of FIFA who were routinely responsible for such contracts, and certainly no mismanagement occurred," he said.
Mr Blatter won a fifth consecutive FIFA presidential election on 29 May but, following claims of corruption, announced his decision to step down on 2 June.
He is due to finish his term at a FIFA extraordinary congress on 26 February.
Fifa cancelled its news conference on Friday only minutes before it was due to start.
Mr Blatter would have been speaking in public for the first time since general secretary Jerome Valcke was suspended last week amid allegations regarding ticket sales at the 2014 World Cup.
Newspaper reports implicated Mr Valcke, 54, in a scheme to sell tickets for above face value.
Mr Valcke, who describes the allegations as "fabricated", has been released from his duties pending an investigation.
FIFA also announced earlier that it had moved its next executive committee meeting from Tokyo to Zurich.
Correspondents say that, although Mr Blatter has not been indicted, he might be more vulnerable to an extradition request outside of Switzerland.