Ahead of the latest EU summit in Brussels, Boris Johnson voiced his "disappointment" they had not been able to move forward more quickly.
The Prime Minister had previously said that he would walk away from the negotiations unless there was agreement by the time of the two-day gathering in the Belgian capital, starting today.
However, in a call with European Commission president Ursula von der Leyen and European Council president Charles Michel on Wednesday evening, he said he would "reflect" on the outcome of the summit before making a decision.
Meanwhile, Mrs von der Leyen and Mr Michel again reiterated that while the EU still wanted a deal, it could not be at "any price".
Following the call a No.10 spokesman said: "The Prime Minister noted the desirability of a deal, but expressed his disappointment that more progress had not been made over the past two weeks.
"The Prime Minister said that he looked forward to hearing the outcome of the European Council and would reflect before setting out the UK's next steps in the light of his statement of 7 September."
Mrs von der Leyen said they were continuing to work on a deal, but the "conditions must be right" if there was to be an agreement.
"The EU is working on a deal, but not at any price. Still a lot of work ahead of us," she tweeted.
Earlier this month, Mr Johnson and Mrs von der Leyen agreed to "intensify" negotiations in a final push for a wide-ranging agreement covering Britain's relationship with the EU when the current Brexit transition period ends at the end of the year.
However, the EU side has been resisting efforts by the British side to impose a tight deadline in an attempt to force through an agreement.
The UK's chief negotiator Lord Frost is expected to brief Mr Johnson on the negotiations with his EU counterpart Michel Barnier - which have been continuing this week - before a final decision on whether it is worth continuing.
Earlier, Number 10 said progress had been made over the past few days, primarily in technical areas, but that differences still remain, namely over fishing rights.
The Prime Minister's official spokesman said: "Some progress has been made this week, primarily in technical areas of the negotiations, but there are still differences, with fisheries being the starkest.
"We need to get the substance settled and not having a common text to work from has made progress doubly difficult.
"The Prime Minister's 7 September statement was very clear about the significance of 15 October.
"He will need to take a decision on next steps following the European Council in the light of his conversation with President von der Leyen, and on advice from his negotiating team.
"I cannot prejudge what that decision will be."
Mr Johnson had said on 7 September that if there was a lack of agreement by the time EU leaders meet in Brussels on 15 October then he could not see any hope of a deal at all, and both sides should at that stage “accept that and move on”.