The 209 members of Fifa are set to vote for their new president at their congress in Zurich, amid a huge corruption scandal.
Sepp Blatter is seeking a fifth term. His only challenger is Prince Ali bin al-Hussein of Jordan.
The vote comes two days after seven top officials were held in Zurich in a US fraud inquiry that indicted 14 people.
Mr Blatter has faced calls to quit but says he is not responsible for the scandal and is favourite to win.
Both Mr Blatter, 79, and Prince Ali, 39, will have 15 minutes to address the delegates.
Each of the 209 member associations can then vote.
In the first round, a candidate must get two-thirds of the votes to win outright, or 140 votes.
If that is not achieved there will be a second round requiring a simple majority, even though there are only two candidates.
Mr Blatter, in office for 17 years, remains the favourite, with strong support in Asia, the Americas and Africa.
The president of the Nigerian Football Federation, Amaju Pinnick, told the BBC he was 100% convinced Mr Blatter would win.
Mr Pinnick said: “We’ve done our homework. For Africa they have 54 votes and maybe one might slip off and might go to another. But I can assure you in Africa we’ll get a minimum of 50 votes.
“And we know our friends from Asia, our friends from Latin America so I can assure you it’s going to be a good victory for him.”
In opening the congress on Thursday, Mr Blatter addressed the issue of corruption, insisting it fell to him to “fix things”.
He said: “We cannot allow the reputation of football and Fifa to be dragged through the mud and it has to stop here and now.”
But he distanced himself from the scandal, saying: “Many people hold me ultimately responsible for the… global football community… I cannot monitor everyone all of the time. If people want to do wrong they will also try to hide it.”
He said the “actions of individuals” had brought “shame and humiliation on football”.
BBC sports reporter Alex Capstick says that this was vintage Sepp Blatter – blame others for the wreckage, then make a pledge to fix it.
Prince Ali has the support of most of Europe.
Responding to the scandal, he said that Fifa needed leadership that “accepts responsibility for its actions and does not pass blame… and restores confidence in the hundreds of millions of football fans around the world”.
He said: “I am a straightforward person with straightforward ideas and ethics – a person who loves our sport.”
The head of European football’s governing body, Uefa, Michel Platini, was one of those calling for Mr Blatter to quit.
At an emergency meeting with other Fifa confederation heads and Mr Blatter on Thursday, Mr Platini said he had asked the president “as a friend” to resign, saying: “I have had enough – enough is enough, too much is too much.”
The president refused, and the other confederations agreed with him that Friday’s vote should go ahead.
Two criminal investigations were announced on Wednesday.
The US investigation accuses those indicted of bribery, racketeering and money-laundering involving tens of millions of dollars over 24 years since 1991.
It includes allegations of bribes to influence the outcome of bids to stage football tournaments such as the 2010 World Cup in South Africa and the 2016 Copa America in the US.
Two Fifa vice presidents were among those arrested in Zurich.
One of them, Jeffrey Webb, was on Thursday “provisionally dismissed” as head of the Confederation of North, Central American and Caribbean Association Football (Concacaf).
Swiss prosecutors have launched a separate investigation into the bidding process for the World Cup tournaments in 2018 in Russia and 2022 in Qatar.
Many of Fifa’s major sponsors have expressed concern over the investigations.
Coca-Cola, Visa, Adidas, McDonald’s, Hyundai Motor and Budweiser are pressing Fifa to take immediate action to restore its reputation.
Even the UN, which has partnerships with Fifa, said it was “watching what’s going on in Zurich and other places very carefully”.