Former Olympic Council of Ireland (OCI) president Pat Hickey is sharing a prison cell with THG director Kevin Mallon, who is also being detained over the alleged illegal sale of tickets.
Mr Mallon was arrested in Rio over a week ago in possession of hundreds of tickets earmarked for the Olympic Council of Ireland.
Mr Hickey, 71, was detained by Brazilian police on Wednesday.
The pair are being held together in the notorious Bangu 10 Rio prison.
On Saturday, a Brazilian judge said that Mr Hickey was remanded in custody on Friday because he was a flight risk.
The OCI board is due to meet on Sunday evening to discuss the issue.
A spokeswoman for the OCI said it is awaiting the return of some board members from Rio.
Irish broadcaster RTÉ reports that former Olympic silver medal winner Sonia O'Sullivan, the Football Association of Ireland chief executive John Delaney, and head of Swim Ireland Sarah Keane are among the board members due to attend the meeting.
Mr Hickey denies the allegations against him but has stepped down from all his posts temporarily.
He served as head of the Olympic Council of Ireland (OCI) as well as the European Olympic body, and also sat on the executive board of the International Olympic Committee (IOC).
On Friday, Irish Sports Minister Shane Ross announced an inquiry into the ticketing claims, following a meeting with Attorney General Máire Whelan.
The inquiry would be chaired by a retired judge who would be appointed next week, said Mr Ross, adding that he hoped it would complete its work in 12 weeks.
Mr Hickey left hospital in a wheelchair on Thursday night and was taken to a police station in Rio where he gave a statement to investigators, reports say.
He was then denied bail by the Court of Justice, and transferred to prison.
Banged up in Bangu
Bangu penitentiary complex houses some of Brazil's most dangerous inmates and is famous for its bloody gang violence.
It has been the scene of murders and riots and several of its officials have been killed.
In December 2005, a security chief became the fifth official from the jail to be murdered in five years.
In 2013, 27 inmates escaped from the sprawling complex by crawling through the sewage system.
However, a women's jail in the complex hosts an annual beauty contest.
Mr Hickey's colleagues at the Olympic Council of Ireland (OCI) have said they will fully cooperate with any Irish state inquiry into the sale of tickets for Rio 2016.
In a statement on Friday it said Mr Hickey was "receiving his own legal advice and is entitled to natural justice and due process".
It said independent legal advisers had been appointed to advise the council's board.
It added that it "would cooperate fully with a state inquiry and it will now appoint an external independent firm to carry out a review".
The council said its board regretted that "recent events in Brazil have overshadowed the many great performances of Team Ireland at the Rio Olympic Games".
The OCI said it would also commission its own independent inquiry into the ticketing scandal.
Who's who in Irish Olympic tickets controversy?
- Olympic Council of Ireland (OCI) - The state-funded body responsible for selecting, training and preparing Irish athletes to take part in the summer and winter Olympics
- International Olympic Committee (IOC) - The leading organiser of the Olympic games and the highest authority in the Olympic movement
- Pat Hickey - The president of the Olympic Council of Ireland
- THG Sports - A corporate and sports hospitality company based in London
- Pro 10 Management - An Irish sports management company that was appointed by the OCI as its authorised ticket reseller in Ireland
- Shane Ross - The Irish sports minister
Mr Hickey was dramatically arrested on Wednesday in his hotel room over his alleged role in a scheme to sell Olympic tickets for a higher price than their face value.
He was escorted off the premises wearing his dressing gown to face questions.
But he complained of heart problems and spent time in Samaritano Hospital in Rio de Janeiro before being taken to a police station for questioning on Thursday night.
William O'Brien, who has temporarily taken over as president of the OCI, said on Thursday that the organisation would "defend ourselves to the hilt".