International Olympic Committee (IOC) board member Patrick Hickey has stepped down after being arrested by police in Rio over alleged illegal ticket sales.
Mr Hickey, who is also president of the Olympic Council of Ireland (OCI), was arrested on Wednesday (local time) at his hotel and taken to hospital after feeling unwell.
In a statement the OCI said he had complied fully with the terms of a police warrant and would continue to co-operate with any ongoing inquiries.
"In light of this morning's developments and his ill health, Mr Hickey has taken the decision to step aside temporarily as president of the OCI and all other Olympic functions," the statement said.
The IOC has also promised to co-operate fully with authorities after police said they had evidence linking Mr Hickey to an international scheme to illegally pass Olympic tickets to touts who were reselling them at well above their original price.
Local reports said Mr Hickey was charged with ticket touting, forming a cartel and illicit marketing.
Spokesman Mark Adams told reporters the IOC was waiting to hear directly from police in relation to the allegations but would co-operate fully with local authorities and had complete faith in the Brazilian justice system.
"Mr Hickey is entitled for the world and everyone to believe he is innocent until proven guilty," Mr Adams said.
"Let's not jump the gun on this one."
Mr Hickey was a member of the IOC's co-ordination commission for the Rio Games, the body in charge of overseeing preparations for the first Olympics held in South America.
His arrest comes after police last week detained a director of international sports hospitality company THG Sports, Kevin Mallon, and a translator employed by the company.
It's alleged they could have made 10 million reais (NZ$4.30 million) from buying tickets and reselling them at a higher price.
A Brazilian judge on Monday also ordered the arrest of four more THG Sports executives on accusations of fraudulent ticket sales at the Olympics.
THG has rejected the accusations against the company and Mr Mallon, saying that more than 1000 tickets seized by police were being held legally on behalf of authorised Irish reseller Pro 10.