FBI probe allegations that Blatter knew of $100mn FIFA bribes
It's alleged that sports marketing company ISL paid officials, including ex-FIFA president Joao Havelange and former FIFA executive Ricardo Teixeira.
In return, the company received television and marketing rights during the 1990s.
Blatter claims he was unaware of the payments, but it's understood the FBI has obtained a letter written by Havelange, who notes that Blatter had "full knowledge of all activities" and was "always apprised" of them.
Havelange was Blatter's top deputy before being replaced by him as FIFA president in 1998.
Blatter has also become the target of a Swiss criminal investigation over possible mismanagement at FIFA and a $2 million payment made in 2011 to his possible successor, UEFA boss Michel Platini.
The probe triggered FIFA's internal ethics watchdog to launch a further inquiry.
FIFA investigators finished their investigation in November, handing evidence over to the ethics committee's judges who will issue a verdict this month.
Platini is allegedly implicated in the same probe and investigators have called for a lifetime ban against him, but the requested punishment against Blatter is not yet known.
US prosecutors are investigating several top football officials as they bid to root out corruption at FIFA.
During the last few days, 16 officials were charged in what the US Justice Department called an "outrageous" betrayal of trust by those who govern football.
Eight people implicated in US investigations have already pleaded guilty, but Attorney General Loretta Lynch has said there are 27 defendants from within global football alleged to have taken more than $200 million in bribes and kickbacks over decades.
Ex-FIFA vice president Jack Warner has accused the US of trying to "take over" FIFA with its anti-corruption investigations, alleging the country is seeking to strip Qatar and Russia of their upcoming World Cups.