The Swiss prosecutor said in a statement that "the defendant Joseph Blatter" had been questioned and "the office of the Fifa president has been searched and data seized".
Blatter was questioned as "a suspect". The statement added that Platini had been questioned "as a person called upon to give information".
Platini, 60, has been head of Uefa since January 2007 which made him an automatic Fifa vice-president. His office refused to make an immediate comment on the Swiss case.
Blatter is suspected of making a "disloyal payment" to Platini at the "expense of Fifa". The alleged payment was made in February 2011 "for work performed between January 1999 and June 2002".
Platini is a former Blatter ally who turned against the veteran Swiss sports baron over the past 18 months as Fifa's troubles mounted.
The investigation is also probing Blatter's links with Jack Warner, a former Fifa vice-president now at the centre of a US investigation into football corruption.
The attorney general said Blatter was suspected of making a deal "unfavourable to Fifa" with the Caribbean Football Union, which Warner used as his power base.
A Trinidad court yesterday announced that it would rule on December 2 on whether Warner should be extradited to the US. The court rejected Warner's request to be freed.
Warner is one of 14 football officials and business executives charged by US prosecutors of involvement in more than US$150 million ($235 million) in bribes for football broadcasting and marketing deals. Nearly all the suspects are from Central and South America.
Until recent days, Fifa's top leadership had escaped accusations flying around the world body, who earn US$5 billion ($7.8 billion) from the World Cup.
Swiss officials arrested seven Fifa officials, who are among the US suspects, on May 27 in Zurich just ahead of the world body's congress. Blatter was re-elected to a fifth term at the congress despite the storm but then announced on June 4 that he would stand down.
Since then, Fifa have announced steps to make reforms but been shaken by new corruption claims.
Fifa this week suspended Blatter's right-hand man Jerome Valcke after he was accused of involvement in an accord to sell tickets for the 2014 World Cup at inflated prices. Valcke strongly denied the allegations but Fifa handed over emails from the suspended secretary general that had been demanded by the Swiss attorney general.
He is also under suspicion over what he knew about a US$10 million ($15.7 million) payment from the South African FA to an account controlled by Warner through Fifa in 2008. US prosecutors believe it was a bribe intended to get Caribbean support for South Africa's bid for 2010 World Cup.
Swiss prosecutors are also looking into Fifa's award of the 2018 and 2022 World Cups to Russia and Qatar respectively. Both have strongly denied any wrongdoing in their campaigns to secure the tournaments.
US attorney general Loretta Lynch said this month her department's inquiry was growing and more charges could be expected. AAP
