Former Taoiseach Bertie Ahern has predicted a new government will not be formed before the end of March.
He said work on creating a “stable and sustainable” coalition had not yet properly begun.
A Sinn Féin surge during last weekend’s General Election on a manifesto promising change in housing and health saw it become the third major party in Ireland.
The first meeting of the Dail parliament on Thursday is unlikely to elect a new government.
Mr Ahern told RTÉ’s The Week in Politics: “When you are putting a Government together we have to look to the future as well.
“It is not just about sorting out the present position.
“It will have to take into account the election result and what is the policy formulation.”
He said negotiators and party strategists needed to focus on housing, homelessness and health.
“Otherwise they will lock themselves into a major problem.”
While Taoiseach and Fianna Fáil leader, Mr Ahern helped create the 1998 Good Friday Agreement which largely ended violence in Northern Ireland.
Sinn Féin topped the first preference poll following this month’s election.
Its total of 37 seats is one fewer than that of Fianna Fáil.
Taoiseach Leo Varadkar’s Fine Gael won 35 seats.
No single party has enough seats to govern and Sinn Féin appears to have failed to muster enough support from a coalition of small left-leaning parties and independent members of the new parliament.
Fianna Fáil has ruled out entering a coalition with Sinn Féin because of historic links to the IRA and wide policy differences over issues like how to run the economy.
It is reportedly veering towards discussions with Fine Gael aimed at forming a grand coalition of two parties from opposite ends of Ireland’s Civil War divide a century ago.
The pair have dominated power since the state’s formation.
On Saturday, Sinn Féin president Mary-Lou McDonald blasted “arrogant” political rivals for denying her party a place in the next Irish government.