Fifa president Sepp Blatter has been questioned by Swiss federal police over alleged financial corruption.
The attorney general's office in Switzerland said it has opened criminal proceedings against Mr Blatter over possible criminal mismanagement and misappropriation of Fifa money.
The Swiss federal office said Mr Blatter was interrogated after chairing a meeting of Fifa's executive committee on Friday.
Fifa vice-president Michel Platini was questioned as a witness over a suspected "disloyal payment" of two million Swiss francs he allegedly received from Mr Blatter in February 2011, Swiss authorities said.
Under Swiss law, a payment is classified as disloyal if it is against the best interests of the employer - in this case Fifa.
Mr Platini is the favourite to succeed the outgoing Mr Blatter as Fifa president next February.
Mr Blatter is the first person to be formally quizzed as a suspect in the Swiss case, which Fifa instigated last November when it complained about possible money laundering in the 2018-2022 World Cup bidding contests won by Russia and Qatar.
The allegations also relate to World Cup broadcasting contracts Mr Blatter agreed to with former Fifa vice-president Jack Warner in 2005.
"There is a suspicion that, in the implementation of this agreement, Joseph Blatter also violated his fiduciary duties and acted against the interest of Fifa," the Swiss federal office said.
The announcements came as Fifa wrapped up a two-day executive committee meeting and marked another stunning day of turmoil for the governing body and Mr Blatter, who have been targeted by American and Swiss investigations into corruption.
Mr Blatter, 79, is set to step down in February as a result of those probes, but the opening of formal proceedings against him could lead the Fifa ethics committee to provisionally suspend him from duty.
The American probe rocked Fifa on May 27, when senior officials suspected of bribery and racketeering were arrested in dawn raids at a luxury Zurich hotel two days before Mr Blatter's re-election.
Mr Blatter is a stated target of that case but has always denied being corrupt, blaming individuals who are outside of Fifa's control
Fifa later issued a statement saying the Swiss attorney general "conducted interviews and gathered documents pursuant to its investigation", adding that it was co-operating with the probe.
Mr Blatter's US-based lawyer, Richard Cullen, said in a statement his client was co-operating and that "certainly no mismanagement occurred".