Senior Ulster Unionist Sir Reg Empey is expected to announce his bid for the party's leadership in Belfast.
Sir Reg is expected to enter the Ulster Unionist leadership race
Former leader David Trimble resigned his leadership after the party lost all but one of its Westminster seats in the May general election.
Sir Reg will be accompanied by several party members when he officially puts his name forward on Thursday.
Sir Reg, the former Northern Ireland enterprise minister, is an assembly member for East Belfast.
On Wednesday, Ulster Unionist peer Lord Kilclooney indicated he would be prepared to back an external candidate to lead the party after next April.
The former MP, John Taylor, made his comments in a statement which ruled out any possibility of him standing as permanent leader of the party.
He mentioned Colonel Tim Collins as one of a number of possible candidates.
But Colonel Collins ruled himself out, saying he was "not qualified to undertake such a momentous position".
Lord Kilclooney said the leadership names suggested so far did not reflect the "radical new approach the party needs".
The Ulster Unionist Council meets on 24 June to elect his successor.