The poll is seen as crucial to repairing the organisation's reputation, which has been battered by a series of unprecedented corruption scandals, but just two days before the vote, protests over the secrecy of ballots have mounted.

Front-runners Infantino -- the Swiss-Italian acting chief of European football -- and Sheikh Salman of Bahrain, Asian football's president, have so far stayed clear of the controversy over balloting. Both were in FIFA's home city of Zurich trying to assemble the coalition of supporters needed to replace the disgraced Sepp Blatter and win the most powerful job in world football.

But rival candidate Prince Ali bin al Hussein of Jordan has appealed to the Court of Arbitration for Sport (CAS) to suspend Friday's election.

He has said transparent voting booths must be used to ensure that delegates do not take pictures of their ballots, a move required by certain regional confederations as proof of loyalty to a specific candidate, according Prince Ali.

"I want this election to occur as soon as possible, but not at the risk of undermining its integrity," the Jordanian royal said in a letter to FIFA's member associations. Jerome Champagne of France, who along with South Africa's Tokyo Sexwale rounds out the list of five presidential challengers, has joined the Jordanian prince's call for greater transparency.

The Lausanne-based CAS has asked FIFA to respond to Prince Ali's concerns and said it will rule on his request for "urgent provisional measures" by Thursday, although it was not clear if the court could force a vote delay.

As closed-door campaigning continued at the luxury Zurich hotels favoured by football power-brokers, FIFA's top brass met for a final pre-election meeting at the body's headquarters on the outskirts of the city.

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