Uefa chief Michel Platini was backed by European football's governing body in his bid to become Fifa president as a new contender emerged.
Asian football chief Sheikh Salman bin Ebrahim Al Khalifa is set to announce he will join the contest.
Platini is alleged to have been paid £1.35m by outgoing president of world football's governing body Sepp Blatter.
The 79-year-old is under criminal investigation over the 2011 payment. Both deny any wrongdoing.
Analysis from BBC sports editor Dan Roan
"While Uefa has tried to present a united front in support of their beleaguered president, behind-the-scenes European football associations know that the Fifa presidential chances of Michel Platini are now in jeopardy, hence the late arrival of Sheikh Salman to the election race.
"The head of Asian football has been given crucial support from leading Uefa figures, along with other parts of the footballing world, and although seen as a compromise candidate, will quickly become a serious contender to replace Sepp Blatter once he declares he is running next week.
"Many critics will still say it is time for the sport to be led by an outsider, but Salman is relatively untainted by past Fifa corruption scandals, and is seen as a credible alternative to Platini and current favourite, Prince Ali of Jordan.
"However, he is not without controversy. Salman led the Fifa taskforce which led to the 2022 World Cup being moved to winter. And human rights groups have alleged he was involved in the arrest and torture of Bahraini players following the 2011 pro-democracy demonstrations in the country. Salman has always denied any wrongdoing."
'Full support' for Platini
Uefa's 54 members met in Switzerland on Thursday to discuss the issue. Platini should have the chance "to clear his name", a Uefa statement said.
It also called for investigators to "work rapidly" and decide "on the merits of the case by, at the latest, mid-November 2015".
Outside the Uefa meeting reporters were told by Austrian soccer federation president Leo Windtner that all 54 member nations "fully support" their president.
The statement issued shortly afterwards confirmed: "We support Michel Platini's right to a due process and a fair trial and to the opportunity to clear his name."
However, one Uefa source told the BBC there was a clear split between those members who continue to back Platini and those who want "to consider a plan B".
Michael van Praag, head of the Dutch FA, is being considered as an alternative candidate to Platini by some member associations - who, the BBC has learned, could hold a meeting on Monday or Tuesday to discuss that option.
Platini is also a vice-president of Fifa, but was last week suspended from all football for 90 days by the organisation while it investigates the payment from Blatter - who was also suspended.
The absence of a written contract detailing the payment had caused several countries to reconsider backing Platini in February's Fifa presidential elections.
Asked by BBC Sport about the payment and his future, before Thursday's emergency meeting, Platini refused to comment.
The former European footballer of the year 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.
An unprecedented situation
Earlier on Thursday, Prince Ali bin al-Hussein of Jordan revealed he had officially submitted his candidature for the Fifa presidency, after insisting February's election should proceed as planned.
Bahraini Salman had given his backing to Platini but is reported to have lost faith in the Frenchman and decided to run himself.
News of his decision to run came on the same day that acting Fifa president Issa Hayatou, who is standing in for the suspended Blatter, arrived in Zurich to start his role.
In an address, he told the organisation's staff they are in "an unprecedented situation".
He added: "We remain focused on the necessary reform process, the presidential election and on supporting the current investigations. To restore public trust is a crucial objective."
A Fifa spokesman said the Cameroonian, who heads the African football confederation (CAF), was updated on "the main administrational matters" - such as the forthcoming Under-17 World Cup and Fifa Club World Cup tournaments.
Acting secretary general Markus Kattner, who provided the update, is himself standing in for the suspended Jerome Valcke, who is banned pending the outcome of another corruption probe.
Meanwhile, the Fifa reform committee that was set up following the arrest and indictment of seven Fifa officials in Zurich earlier this year is to hold its second meeting on Friday.
One of those seven, former Nicaraguan Football Federation president Julio Rocha, had his extradition to the United States approved by Swiss authorities on Thursday, although he has 30 days to appeal against the decision.