The UUP leader says the prospect of a pre-Christmas Assembly election is "absolutely diabolical".
Doug Beattie was speaking after talks with the new secretary of state, Chris Heaton-Harris, on Tuesday.
"I think an election in the winter would be absolutely diabolical, but if that is what has to happen that is what will happen," said Mr Beattie.
Earlier, Mr Heaton-Harris had a phone conversation with Alliance Leader Naomi Long, and he's scheduled to meet SDLP Leader Colum Eastwood in London this week.
The talks have been focused on restoring Stormont's power-sharing institutions, and dealing with the cost of living crisis.
The DUP is currently blocking the functioning of the Executive as part of its protest against the Northern Ireland Protocol.
Current rules stipulate that without a functioning Executive, ministers must stand down on 28 October and the Government call an election within 12 weeks.
"That means there has to be an election by 19 January," said Mr Beattie.
"That is the process. There is no other process so we would expect to have an election on either December 8 or 15."
Mr Beattie says he hopes that some goodwill created by the death of the Queen could be used in new negotiations between the EU and UK over the Protocol.
"I got a sense that the sad circumstances of the last number of days has created a degree of goodwill and there is going to be new impetus put into negotiations between the UK and the EU in regards to the Northern Ireland Protocol, and a change in language I think," he said.
"Northern Ireland cannot be treated differently from the rest of the United Kingdom, but having no executive is incredibly difficult."
Political opponents of the DUP have heavily criticised the party's boycott, insisting it is hampering efforts to support families struggling amid the cost-of-living crisis.
The Government has vowed to secure changes to the protocol, either by way of a negotiated compromise with the EU or through controversial domestic legislation that would empower ministers to scrap the arrangements without the approval of Brussels.
Mr Heaton-Harris became secretary of state two weeks ago when he was appointed to the role as part of Prime Minister Liz Truss's new Cabinet.
He's previously said the restoration of the Executive is his priority.
The Northern Ireland secretary met Sinn Fein and DUP representatives shortly before the death of the Queen led to the pausing of political negotiations.
He had been criticised at the time for not meeting the smaller parties.
Sinn Féin Stormont leader Michelle O'Neill said she had stressed to Mr Heaton-Harris that people in Northern Ireland are desperate for the restoration of the Executive, while DUP Leader Sir Jeffrey insisted his party was under no pressure from the Government to re-enter power-sharing.
The new secretary of state also met King Charles last week when the new monarch visited Hillsborough Castle.