She says nobody could expect Irish people "to simply go along with" a crash Brexit
Sinn Féin leader Mary Lou McDonald has said a no-deal Brexit would increase the pressure for a poll on a united Ireland.
Reports from the UK have claimed the Northern Ireland secretary Karen Bradley told the British cabinet this week that a no-deal exit from the EU would increase the chances of an Irish reunification referendum, under the terms of the Good Friday agreement.
Mrs Bradley has refused to comment on the reports, although told BBC that a no-deal Brexit would likely create a "feeling of unrest" among those in the UK who didn't want to leave the EU.
Deputy McDonald today said her party has frequently told the British government they believe Ireland is on the path to a border poll - Brexit or no Brexit.
Speaking in Dublin, she argued: "There is no doubt that the prospect of a crash Brexit means the issue of putting the constitutional question is on the table.
"I welcome the fact that Karen Bradley seems to recognise that you couldn't have a crash Brexit - with all of the damage that would entail for our island - and expect Irish people to simply go along with that, to simply absorb all of that damage."
She added: "I hope there isn't a crash, but in the event of that happening... of course there will be an onus on the British government to put the constitutional question... there'd be an onus on the Dublin government to seek that poll.
"In any event, given the direction of Irish political life and progress, I believe those preparations need to be in train anyhow."
MPs in the House of Commons are due to vote on the Brexit withdrawal dealing this coming Tuesday - a vote Theresa May's government is widely expected to lose.