FIFA Secretary General Jérôme Valcke has been put on leave and released from his duties with immediate effect following allegations over World Cup tickets.
A statement on the international football organisation's website said it had become aware of "a series of allegations" involving Mr Valcke and had requested a formal investigation by the FIFA ethics committee.
Emails and documents seen by journalists earlier on Thursday suggest Mr Valcke signed-off contracts with a Swiss marketing company that was selling thousands of tickets at five times their face value.
Sky News sports correspondent Paul Kelso said: "This isn't his first encounter with difficult allegations but it has come of something of a surprise that FIFA should have taken decisive action over this.
"It follows allegations by a former ticket agent, Benny Alon, that Mr Valcke was party to a deal to sell more than 8,000 tickets at the World Cup and profit on the proceeds; a clear conflict of interest if proven."
Mr Alon claims he sent an email to Mr Valcke in April 2013 detailing how much was being made on each ticket - the biggest mark-up being 50 tickets for a second-round match in Sao Paulo with a face value of $230 being sold for $1,300 each.
A statement from Mr Valcke's US-based lawyers said he "unequivocally denies the fabricated and outrageous accusations by Benny Alon of alleged wrongdoing in connection with the sale of World Cup tickets".
Earlier this year seven FIFA officials were arrested in Switzerland over allegations they were part of a racket involving bribes adding up to more than $150m (£96m).
Swiss authorities detained the officials - two FIFA vice presidents and five other current or former senior FIFA officials - in an early-morning operation in Zurich on suspicion of receiving and paying bribes.
Former FIFA vice president Jack Warner also surrendered to police in Trinidad after an arrest warrant was issued at the request of US authorities.
In July Mr Valcke said he would likely leave his role when Sepp Blatter also steps down as president of the governing body next year.
