Patrick Hickey, a senior member of the International Olympic Committee, has temporarily stood down from all his roles after his arrest in Rio over allegations of illegal ticket sales.
The Irishman, 71, was taken to hospital following his arrest, after requesting medical attention.
Brazilian police claim he was involved in a scheme to resell Olympic tickets at higher than their face value.
They said the scheme could have had profits of 10m reals (£2.4m; $3.1m).
Mr Hickey will be replaced as president of the European Olympic Committees - the body which brings together the 50 national committees across the continent - by his deputy Janez Kocijancic.
The Olympic Council of Ireland (OCI) said in a statement that Mr Hickey was stepping aside 'until this matter is fully resolved' and would continue to co-operate and assist with all enquiries.
The former judoka has been a member of the 15-strong executive board of the International Olympic Committee since 2012, making him a prime mover in the world of international sports.
Police said the arrest was related to that of fellow Irishman Kevin James Mallon on the day of the Olympic opening ceremony.
More than 700 tickets organised in envelopes clearly marked for sale were found in a safe with Mr Mallon, Detective Ricardo Barbosa told the BBC.
Police had evidence of a plan to sell tickets 'illegally masked as hospitality packages,' Mr Barbosa said.
Irish broadcaster RTE reports that Mr Hickey faces three potential charges: facilitating ticket touting, forming a cartel, and 'ambush ' or illicit marketing.
In an interview with RTE last week, Mr Hickey denied any wrongdoing in relation to ticket sales.
![]() Mr Mallon, who has been in custody since his arrest on 5 August, is a director of THG Sports, a British corporate and sports hospitality company owned by Ipswich Town Football Club owner Marcus Evans.
THG Sports rejects the allegations, saying Mr Mallon had not sold or sought to sell tickets but had been holding them for collection by clients of the authorised Irish ticket reseller, Pro 10 Management.
Pro 10 Management also denies any wrongdoing, saying in a statement released on 12 August that it had always acted properly and fully in line with the guidelines.
Detective Barbosa told the BBC that investigators believed 'Pro 10 was created as a means for acquiring tickets to be resold by THG' as the Irish Olympic Committee had wanted THG to sell tickets for Rio 2016, he alleged.
On Monday Brazilian authorities issued arrest warrants for four people connected to THG, including Marcus Evans, the British multi-millionaire who owns THG Sports' parent company and Ipswich Town Football Club.
A further three arrest warrants were issued on Wednesday for directors of Pro 10 Management, Brazilian police said.
The International Olympic Committee (IOC) said it would co-operate with any police investigation and stressed that Mr Hickey should be presumed innocent until proved otherwise.
Vocabulary judoka: 柔道运动员 |
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