Former Taoiseach Bertie Ahern believes it is inevitable that there will be a border poll in the next ten years.
Sinn Féin say they will provide a vote in the next five years if they are able to form a government.
The Good Friday Agreement provides a procedure for the reunification of the island but only with the approval of the electorate in both the Republic and Northern Ireland.
Speaking to LBC this morning, Mr Ahern said there is a lot of work to get through first.
He said: "There will be a vote on that issue in the next decade, I think that is inevitable.
"What the result of that vote will be, it'll have to be a vote in the north, it'll have to be a vote in the south, is a different question.
"I think the outcome will be very much based on the case that's made following qualitative and analytical work that's done and that job still has to take place."
Last week, Mr Ahern said he does not believe a large number of Fianna Fáil TDs would back a coalition with Sinn Féin.
He also told Newstalk Breakfast that there's unlikely to be support for a Sinn Féin alliance if Ms McDonald fails to put together a left-leaning government.
Mr Ahern suggested that Sinn Féin is in the 'driving seat' going into the government formation talks, adding that he believes a Fianna Fáil and Fine Gael arrangement would lead to a 'large reaction from the people'.
However, Sinn Féin TD Louise O'Reilly said today she believes another election is a real possibility after there was "not a huge amount of progress" made during a phone call between the Sinn Féin and Fianna Fáil leaders yesterday.
