Michel Platini is being treated as "between a witness and an accused person" and the Swiss authorities would raid the UEFA president's office if necessary to discover the "real truth," the attorney general said Tuesday.
Platini was questioned on Friday about a 2011 payment from FIFA which led to a criminal case being opened against Blatter, who was quizzed as a suspect.
Platini said on Tuesday that he doesn't "fear a [FIFA] suspension because I have done nothing wrong," with less than a month to go until he must pass integrity checks to stand in the FIFA presidential election in February.
Speaking at Zurich University, Swiss Attorney General Michael Lauber wouldn't be drawn about what might follow for Platini, or the specifics of the case against Blatter for "tactical reasons."
Lauber's team searched Blatter's office and seized data on Friday.
Asked if he would be prepared to raid Platini's UEFA office, Lauber responded: "I will do anything, if I can do something, to clear up what's the real truth and if I have enough elements to go there I could not exclude that I also have to go there."
Blatter was questioned why about why FIFA paid 2 million Swiss francs (about $2 million) to Platini in 2011 for work supposedly carried out at least nine years earlier.
Asked if the authorities were satisfied with Platini's answers, Lauber said: "We did not [question] Mr. Platini as a witness ... we investigated against him as in between a witness and an accused person.
"If I was satisfied or not, I can't tell you because I would do real big damage to the investigation."
Platini, who denies wrongdoing, offered his first explanation on Tuesday as to why there was such a long gap before the payment was made.
"Like I explained to the Swiss authorities, I received only part of the agreed salary between 1998 to 2002," Platini said in comments provided by UEFA. "This occurred because at the time, FIFA informed me that they would not be able to pay me the total agreed amount. Of course, all the moneys received at the time were declared to the pertinent authorities."
FIFA's accounts for 1999-2002 show a revenue surplus of 115 million Swiss francs (about $83 million in 2002).
"Mr. Blatter informed me when I started my role as his adviser [in 1998] that it was not initially possible to pay the totality of my salary because of FIFA's financial situation at that time," Platini said.
"I never doubted, however, that the remaining amount owed to me would be paid eventually, so I did not actively pursue it. I even put the matter to the side for a while, before finally requesting that the outstanding balance was paid in 2011."
Platini denied any link to his support for Blatter in the presidential election in May 2011.
"The fact that this payment was made a few months before the FIFA presidential elections is irrelevant, since I never had any plans of becoming a candidate," Platini said.
Lauber described the ongoing FIFA case as a "big investigation."
"This is not a 90-minute game," he said. "It's like more or less not even at the half-[time] break."