The American diplomat who tried to broker a deal at Stormont has warned a UK exit from the EU could exacerbate tensions in Northern Ireland.
Richard Haass, whose five-month sets of negotiations ended in failure, also pointedly criticised both unionists and republicans for showing they are "unable to face up to the past, or work together in the present".
In his first major comment on politics in the province since he and his talks co-chair professor Meghan O'Sullivan departed just after New Year in 2014, Dr Haass said the "difficult divorce" of a Brexit was the last thing the new American President would need.
His comments came as First Minister Arlene Foster revealed she is hoping to meet Foreign Secretary Philip Hammond to voice concerns over the proposed date for the Referendum, June 23.
On his personal blog, Dr Haass wrote that a decision by the British people to leave the EU "would also put the question of Scotland's independence squarely back on the agenda.
"Indeed, many in Scotland would argue for independence in order to remain an EU member - a popular refrain that could well result in a vote to secede from the UK...
"What happened in Scotland could well have ripple effects across what remained of the disunited United Kingdom.
"In particular, Great Britain's departure from the EU and Scotland's departure from the UK would add to tensions in Northern Ireland between pro-UK unionists and republicans seeking to join Ireland.
"Raising the profile of 'final status' issues at a time when the two sides have shown themselves unable to face up to the past, or work together in the present, is not a recipe for progress."
Dr Haass also argued the timing for the referendum "could hardly be worse" with Europe already facing a "perfect storm of fiscal strains, anaemic economic growth and massive inflows of migrants and refugees.
SDLP leader Colum Eastwood said there was no doubt that a Brexit "would have a divisive influence on a society as fragile as ours. "After years of conflict, it's important that we embrace that which unites us, our common European identity. We must all seek to heal the wounds of the past while laying the groundwork for a prosperous future," he said.
Ulster Unionist leader Mike Nesbitt said his recent US visit had shown America wants a strong United Kingdom within a united European Union.
A Sinn Fein response to the Haass comments said: "Executive ministers have worked to bring thousands of good quality jobs into the North on the basis that we are a gateway to a European market of 500 million Euro."
Mrs Foster, meanwhile, said the March 1 discussions with Mr Hammond could be "too late" with David Cameron planning to negotiate on an EU reform package this Thursday, with a Cabinet meeting the following day.