Members of the FIFA football governing body will vote for their new president at their congress in Zurich, amid a huge corruption scandal.
Incumbent President Sepp Blatter wants a fifth term. His only contender is Prince Ali bin al-Hussein of Jordan.
The vote of the 209 FIFA members comes two days after seven senior US fraud investigators were held in Zurich, bringing charges against 14 people.
Sepp Blatter, 79, is facing calls to leave, but says he is not responsible for the scandal and is the favorite to win.
Both Sepp Blatter and 39-year-old Prince Ali bin al-Hussein will have 15 minutes to address the delegates.
Each of the 209 member associations can then vote.
In the first round, the candidate must receive two-thirds of the votes to win the final, or 140 votes.
If this is not achieved, there will be a second round, requiring a simple majority, although there are only two candidates.
Sepp Blatter, who has been in office for 17 years, remains the favorite with strong support in Asia, America and Africa.
At the opening of the congress on May 28, Sepp Blatter addressed the issue of corruption, insisting that it should “fix things”.
He said: “We cannot allow the reputation of football and FIFA to drag through the mud and it must stop here and now.”
However, Sepp Blatter distanced himself from the scandal by saying: “A lot of people end up holding me for … the global football community … I can’t watch everyone all the time. If people want to make a mistake, they will also try to hide it. “
He said “the actions of individuals” had brought “shame and humiliation to football”.
Prince Ali bin al Hussein has the support of most of Europe.
In response to the scandal, Prince Ali said FIFA needed a leadership that “takes responsibility for its actions and is not to blame … and restores the trust of hundreds of millions of football fans around the world.”
He said: “I am a straightforward person with clear 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 Sepp Blatter to leave.
In an emergency meeting with other FIFA leaders and Sepp Blatter on May 28, Michel Platini said he had asked the president “as a friend” to resign, saying: “I’ve had enough – enough is enough, too much is too much.”
Sepp Blatter refused, and the other confederations agreed with him that Friday’s vote should continue.
On May 27, two criminal investigations were announced.
The US investigation accuses the accused of bribery, racketeering and money laundering, involving tens of millions of dollars in 24 years since 1991.
It includes allegations of bribery to influence the outcome of bidding for football tournaments such as the 2010 World Cup in South Africa and the 2016 Copa America in the United States.
Two FIFA vice-presidents were among those arrested in Zurich.
One of them, Jeffrey Webb, was “suspended” on May 28 as head of the Confederation of North, Central America and the Caribbean Football Association (CONCACAF).
Swiss prosecutors have launched a separate investigation into the bidding process for the 2018 World Cup in Russia and the 2022 tournament in Qatar.
Meanwhile, many of FIFA’s main sponsors have expressed concern about the investigations.
Coca-Cola, Visa, Adidas, McDonald’s, Hyundai Motor and Budweiser are pushing FIFA to take immediate action to restore its reputation.