Northern Ireland is seen as "expendable" by some in Westminster focused on Brexit, the Ulster Unionist leader said.
Robin Swann warned some unionists had become so fixated on the EU divorce they had become "blinkered" to the challenges created for the union of the UK.
He told a Belfast audience: "I am concerned that just as there are those within nationalism who seek to exploit this situation for their own ends, there are unionists who are so focused on our exit from the European Union that they have become blinkered to the challenges being created to the most important Union of all.
"And there are those in Westminster so focused on Brexit that Northern Ireland is seen as expendable.
"This is the danger of relentlessly following ideology and not accounting for the realities."
He warned against damaging the greater good.
He added: "Whether Brexiteer or Remainer, the focus should now be on the solution."
Mr Swann addressed a meeting at the Titanic Hotel in Belfast on the theme of a "stronger union".
He said: "Unionism is not merely a rejection of a different constitutional arrangement.
"It is the ultimate belief that the constitutional settlement we enjoy makes sense and holds values, ideas and commitments that can and will build an inclusive and strong society.
"It is about a partnership that is enduring and allows us to draw on the diversity that Northern Ireland, England, Scotland and Wales bring to economic and cultural success."