She said the debate is part of the 1998 Good Friday Agreement, which states that Northern Ireland's Secretary of State may call for a referendum if it appears likely that the majority of voters would wish to leave the United Kingdom and enter into a united Ireland.
But Simon Coveney said it was not too late to create a plan that would protect the single market and the peace process on the island of Ireland in the absence of a backstop.
McAleese, who was speaking during the Dublin City University (DCU) Brexit Institute Conference on the UK's withdrawal from the European Union, said there is a need to ensure the "groundwork is laid" ahead of any Irish unity referendum.
He said he will use the meetings to discuss the "possible scenarios arising from this week" - including ongoing efforts to secure ratification of the Withdrawal Agreement and the European response to any potential United Kingdom request for a longer extension.
"Any extension must have a clear objective and a clear plan", Varadkar said.
"We will never abandon Ireland or the Irish people no matter what happens, because this solidarity is the very objective of the European project", said Mr Macron.
They were speaking before Mrs May announced that she would seek a further Brexit extension and would be willing to meet Labour leader Jeremy Corbyn to find a way forward to "break the logjam" in the House of Commons.
They both said the integrity of the single market would need to be protected, but that the European Union would uphold commitments made to ensure the protection of the Good Friday Agreement.
The Irish premier met with Macron ahead of talks with Germany's Chancellor Angela Merkel in Dublin.
"We need to talk about what we will do in the event of "no deal", which will be particularly hard for Ireland", Mr Varadkar admitted.
The UK parliament has voted - again - to reject Theresa May's divorce deal from the EU.
Ireland's 500 km (350 mile) border with British-governed Northern Ireland will be the UK's only land frontier after Brexit. "We need to be open to any proposals that she may bring forward to us", adding that as things stood Britain was heading towards a no-deal exit.
Sinn Fein leaders Mary Lou McDonald and Michelle O'Neill met European Union negotiator Michel Barnier and the European Union parliament's Brexit co-ordinator Guy Verhofstadt for discussions in Brussels on Tuesday.
He said his government was now in negotiations with the European Commission as to how to achieve both of these objectives.