Several countries will drop their support for Michel Platini's bid to become the next Fifa president if they do not get assurances over a £1.35m payment made to him by Sepp Blatter.
Outgoing Fifa boss Blatter is under criminal investigation over the 2011 payment, while Uefa president Platini has been questioned about it.
Blatter and Platini deny wrongdoing.
The 54 members of European football's governing body Uefa meet in Switzerland on Thursday to discuss the issue.
The absence of a written contract detailing the payment has caused several countries to reconsider backing Platini in February's Fifa presidential elections.
Dutch, German and Danish officials have all gone on the record to say they will be seeking assurances over the payment at the meeting in Nyon.
The English Football Association has maintained its "unanimous" support for Platini, but added it was "following the ongoing investigation".
Asked by BBC Sport about the payment and his future, before Thursday's emergency meeting, Platini refused to comment.
Prince Ali bin al-Hussein of Jordan has officially submitted his candidature for the Fifa presidency, after insisting February's election should proceed as planned.
|Analysis - BBC sports editor Dan Roan|
|"It has not gone unnoticed that according to Fifa's 2002 official finance report between 1999 and 2002 the organisation enjoyed surplus revenue of 115m Swiss francs (about £80m at the time), making it hard to accept that the body could not afford to pay Platini his fees.|
|"What also makes all this so awkward is that shortly after Platini received the money in 2011, he backed Blatter's re-election as Fifa president, deciding not to stand against him."|
Frenchman, Platini, 60, has said he accepted the sum as delayed payment for work carried out as Blatter's adviser between 1998 and 2002. But the nine-year delay in receiving the rest of the payment has caused concern for some Uefa members.
Both men were suspended for 90 days by Fifa's ethics committee in early October while it investigates the corruption allegations.
That came after the Swiss attorney general opened criminal proceedings against Blatter, 79, who has said the payment to Platini was "valid compensation and nothing more".
Platini said he was spoken to about the payment by Swiss investigators, who later said the Frenchman was "between a witness and an accused person".
Blatter is also accused by Swiss prosecutors of signing a contract that was "unfavourable" to world football's governing body.
That is believed to be a 2005 TV rights deal between Fifa and Jack Warner, the former president of Concacaf - the governing body of football in North and Central America and the Caribbean.
Meanwhile, the Fifa reform committee that was set up following the corruption scandal that engulfed world football's governing body earlier this year is to hold its second meeting on Friday.