Former Olympic Council of Ireland (OCI) president Pat Hickey is sharing a prison cell with Kevin Mallon, the director of THG, who is also caught up in the ticketing investigation.
Mr Hickey is facing allegations of the illegal resale of tickets for the games. He denies any allegations that he was involved in ticket touting.
Mr Mallon was arrested in Rio over a week ago in possession of hundreds of tickets earmarked for the Olympic Council of Ireland.
He is an executive with sports hospitality company THG which does not have the licence to sell Ireland's Olympic tickets.
The Authorised Ticket Reseller is Pro 10 Sports Management.
Now the pair are sharing a cell and getting the same food and standard haircut as the other inmates, a prison official said today.
Rio's Bangu prison complex, which has more than a dozen separate units in the city's rough western reaches, is notorious for violence and uprisings.
Meanwhile, Mr Hickey has not yet been heard by a judge and should be presumed innocent, IOC President Thomas Bach said today.
"What we know is that he has not been heard by a judge yet and, more so, the presumption of innocence prevails," Mr Bach told a news conference during the closing weekend of the Rio Games.
"We respect the laws and legal procedures here in Brazil and cannot comment further on this," added Mr Bach.
Hickey remanded over flight risk, says judge
Earlier, a Brazilian judge said that Mr Hickey was remanded to custody because he was a flight risk.
In a statement, published on the Rio de Janeiro Courts Service website, the judge who signed the order to imprison Mr Hickey, said she had done so, to avoid the accused leaving the country.
Judge Mariana Tavares Shu cited the case of James Sinton, from the Marcus Evans group, who was arrested during the World Cup in Brazil in 2014.
Mr Sinton was awarded bail and left the country. He has not returned since and therefore has not answered to the charges laid against him two years ago.
Justice Shu said: "Pre-trial detention ensures the expediency of criminal prosecution, and the application of penal law. Since all of those involved are foreigners, and do not have fixed addresses in the country, in a way that makes it foreseen that, if they remain free, may leave the jurisdiction."
Speaking about Mr Sinton, Justice Shu said: "…as soon as he was released, returned to his country of origin."
A spokesperson for the Rio de Janeiro Courts Service said yesterday that a bail application for Mr Hickey was lodged with the courts, which despite being in recess for the games, still acts in emergency cases.
The Rio de Janeiro court found that the order for Mr Hickey's detention was "well-founded", and denied the bail application.
As to how long Mr Hickey could be held at Bangu Prison, the Rio Courts Service said the justice system could keep a defendant in custody "until a judge decrees that it is no longer necessary for the defendant to be in custody to answer charges".
Mr Hickey’s case will be referred to one of the local criminal courts, after the courts return to normal business on Tuesday (23 August).
Mr Hickey’s team may bring a further bail application to the Supreme Court in the meantime.
In normal circumstances, it takes at least one month before a trial would be held, after formal charges are laid, to allow time to gather witnesses to testify.
Board of OCI to meet tomorrow
Meanwhile, the board of the OCI will meet tomorrow to discuss the controversy.
A spokeswoman for the OCI said the meeting will happen late tomorrow in Dublin, because it is awaiting the return of some board members from Rio.
It is expected the board will make a statement about the events following the meeting.
Former Olympian Sonia O'Sullivan, the FAI Chief Executive John Delaney, and head of Swim Ireland Sarah Keane are among the board members due to meet to discuss the issue.
The meeting will be chaired by the OCI's Acting President Willie O'Brien.
11 of the 12 members of the OCI's Executive Committee will attend tomorrow's meeting.
The board has said it will co-operate fully with a State inquiry and will also appoint an external independent company to carry out a review.
A retired judge is to be appointed by the Government next week to chair a non-statutory inquiry into matter.
Minister for Sport Shane Ross said the terms of reference would be finalised shortly afterwards and that it was hoped it could complete its work in 12 weeks.