Sir Reg Empey has said the UUP was reserving judgment on the Hillsborough deal after refusing to attend the round table meeting with the British and Irish premiers on Friday morning.
We’re sorry. This video is unavailable from your location.
During the negotiations, the UUP leader repeatedly complained that it had been kept in the dark.
Sir Reg told the media he had only received the agreement at 11am on Friday.
After meeting with his assembly group at Stormont, Sir Reg said the party will not be rushed into giving their conclusion to the governments.
"We have no alternative but to study the document, take it away, consult and reach a conclusion", he said in an early sign of potential discord.
Sinn Fein and the DUP expect a response by Monday, when the First Minister and Deputy First Minister will consider applications for the new Justice Minister.
But the UUP leader has told UTV the deadline was "totally unreasonable and unrealistic."
"It will take us as long as it takes us", Sir Reg said.
"The truth of the matter is people took whatever length of time over the last 12 days. To give us until Monday is totally unreasonable and unrealistic. We will not be rushed. We will do it right," he told UTV.
The deal suggests a role for the UUP leader as co-chair of a group looking into the dysfunctional nature of the executive, an issue which Sir Reg championed throughout the talks.
"It's unfortunate that I was not approached about that matter and indeed I was not asked if I would undertake the role", he said.
Sir Reg said the party will examine the document "on its merits".
"We're keeping very much in our minds the potential if we get stability here."
The UUP has felt excluded from the discussions in which they were not formally engaged, but "twice on Friday, Peter Robinson said it was essential to have the Ulster Unionists on board, as part of community confidence," UTV's Political Editor Ken Reid noted.
Earlier this week, the UUP leader dismissed talk of a formal link up with the DUP, despite secret talks between the parties.
The UUP and the DUP met at the Orange Order headquarters in Belfast in December 2009.
Further talks were also held at Hatfield House in England in January, chaired by shadow Northern Ireland secretary Owen Paterson.
The UUP executive reaffirmed its commitment to its relationship with the Conservative Party on Tuesday, passing a resolution to agree joint candidates for the forthcoming general election as soon as possible.
Conservative leader David Cameron welcomed the Hillsborough deal.
"We hope this leads to the completion of devolution and the re-establishment of political stability in Northern Ireland," Mr Cameron said.
'Outraged'
The leader of the Traditional Unionist Voice Jim Allister, meanwhile, has firmly condemned the settlement.
While, under the terms of the agreement, neither the DUP nor Sinn Fein will hold the new justice ministry, Mr Allister said he was outraged that the republicans will jointly lead a government responsible for law and order.
"This is a Sinn Fein win and defeat for Unionism", Mr Allister said.
"Even the DUP promise to ensure that the Justice Minister's actions would be protected from the Sinn Fein veto within the Executive has been broken."
Leader of the loyalist Progressive Unionist Party Dawn Purvis welcomed the deal.
"I think it is hugely significant, it is what the people of Northern Ireland wanted, it is what all the political parties wanted. It means we are not facing an election, which would have been absolutely disastrous," she said.
© UTV News