Former Taoiseach Brian Cowen has been hospitalised after becoming seriously ill in recent days.
Mr Cowen is understood to be receiving treatment in a Dublin hospital following concerns regarding his health.
He is believed to have checked into hospital on Thursday and was continuing to receive treatment yesterday.
His family said they would like the matter to be treated as privately as possible.
Yesterday, a number of Mr Cowen's Fianna Fail coll- eagues wished him a speedy recovery and a return to full health.
Taoiseach Leo Varadkar also said he hoped Mr Cowen makes a full recovery after learning he had fallen ill.
Speaking at an event in Longford, Mr Varadkar said: "I served in the Dail with Brian Cowen for a number of years and I really hope, if he is unwell, as I hear he is, that he makes a speedy recovery."
Long-serving Fianna Fail TD and former minister Willie O'Dea said he hoped Mr Cowen recovered as soon as possible.
"I've know Brian since he was one of my students in UCD and we were great friends in politics too," Mr O'Dea said.
"I hope he gets well very soon and makes a full recovery."
Former Fianna Fail deputy leader Eamon O Cuiv said his thoughts were with Mr Cowen and his family.
"I wish him a very speedy and full recovery and I think it is well-known I have great respect for what he did during a very difficult time for this country," Mr O Cuiv said.
"My thoughts are with him and his family at this difficult time."
Justice Minister Charlie Flanagan, who shared a constituency with Mr Cowen for many years, said he was "very sorry to hear" his former Dail colleague had fallen ill.
Mr Flanagan wrote on Twiter: "I wish himself and his family well at this anxious time and worrying time."
Mr Cowen is married to Mary and is the father of two daughters, Sinead and Meadhbh.
He was also taken to hospital in May when he became ill at an Oireachtas golf event.
He was reportedly taken by ambulance to Limerick Regional Hospital after becoming unwell at Lahinch Golf Club in Clare.
He had recovered and attended public events, including the funeral of GAA legend Eugene McGee.
Mr Cowen has kept a relatively low profile since stepping down from national politics.
Along with other former taoisigh, he attended a ceremony for Pope Francis at Dublin Castle during the papal visit to Ireland last year.
In 2017, he was awarded an honorary doctorate by the National University of Ireland.
During a speech at the event, he criticised the EU over its role in the financial crisis and defended measures Fianna Fail had introduced during the crash.
Last February, he criticised Britain's approach to Brexit negotiations during an appearance in Belfast.
He said the view of certain Conservative Party MPs on the controversial backstop was "unreasonable".