US prosecutors reportedly believe that Sepp Blatter's deputy ordered $10 million to be paid to a football official accused of accepting bribes in return for awarding the 2010 World Cup to South Africa.
According to the New York Times, the US government has evidence that Jérôme Valcke, the secretary general of Fifa, ordered the money to be paid into accounts controlled by one of the nine football executives indicted last week. He denies this.
The claim, if proven, would mean that Mr Blatter's closest lieutenant was connected to the bribery scandal and raise fresh questions for the recently re-elected Fifa president.
Mr Valcke, a Frenchman, is a close ally of Mr Blatter and was appointed general secretary of football's global body in 2007 at Mr Blatter's suggestion. The two men clasped hands after Mr Blatter won re-election to his post last week.
US prosecutors allege that the South African government paid $10 million in bribes to Jack Warner, the head of the Caribbean Football Union, and other football officials in order to secure their votes for South Africa to host the 2010 World Cup.
The payments were allegedly disguised as money "support to the African diaspora".
The US alleges that when South Africa was unable to pay the money directly to Mr Warner "a high-ranking Fifa official" ordered the payments to be made from Fifa's accounts.
Mr Valcke denied to the New York Times that he was the "high ranking official" and said he did not have the authority to order the payments.
Mr Valcke has not been charged with any crime nor has the US made any public allegations against him.
While the US indictment refers to multiple anonymous "co-conspirators", who are accused of a crime but not publicly named, the "high ranking official" is not alleged to have broken US law.
The US has said repeatedly that it is only at the beginning of its investigation into corruption in world football and that more officials may eventually face charges.
December 2010, the eve of the vote for the 2018 and 2022 World Cups. Speculation has reached fever pitch in the Baur au Lac lobby as royalty, heads of state and breathless football executives criss-cross the room to genuflect before the 22 voting members of the Fifa executive committee.
Is the overriding principle of our times that bad behaviour drives out good? The assertion of self-interest and the pursuit of profit, by fair means or foul, trumps everything. Great values are under assault. Whether nobility of purpose, behaving with integrity, looking out for others, accepting responsibility or just doing the right thing - all seem to be withering on the vine.
Here's why FIFA corruption really matters. Wednesday's arrest of nine of the organisation's leading officials and four sports management executives who the US Department of Justice claim have received over $150m in bribes over the past 24 years is only the beginning.