Cabinet minister Michael Gove has said the chances of the UK and EU agreeing a post-Brexit trade deal are “less than 50%”.
Earlier, the EU’s chief negotiator, Michel Barnier, tweeted “good progress” had been made on a deal.
But Mr Gove told MPs “regrettably the chances are more likely we won’t secure an agreement”.
Talks in Brussels are continuing on Thursday, with two weeks to go before the UK leaves EU trading rules.
European Parliament leaders have set Sunday as a deadline for them to see the text of any deal.
The senior MEPs said they would “not be rushed” into approving an agreement at their end, and would have to see the text by the end of the week if they were to sign it off by 31 December.
MPs from the UK Parliament have been warned by Mr Gove they could be called back during their Christmas break to ratify a any deal that emerges from talks.
The UK left the EU on 31 January, but has remained under many of its rules while the two sides negotiate a trade deal.
If an agreement is not reached by 31 December, the UK will have to trade with the EU on World Trade Organization rules – meaning taxes on goods being bought and sold between the two may be introduced, and could lead to higher prices.
Michel Barnier said the talks were in their final stages and the “last stumbling blocks remain”.
But Mr Gove echoed the comments of Prime Minister Boris Johnson’s spokesman on Wednesday, who said he still viewed no deal as “the most likely outcome”.
Mr Gove made the comments while appearing in front of MPs at the Future Relationship with the European Union Select Committee.
Asked if a deal could be reached before the Sunday deadline set by European Parliament leaders, he said: “My new resolution adopted from a few weeks ago is to avoid giving percentages.
“But I think at the moment actually… regrettably chances are more likely we wont secure an agreement, so at the moment less than 50%.”
Mr Gove earlier told the Commons that the government was “doing everything in order to secure a good free trade agreement in the interest of the whole United Kingdom”.
It’s long been predicted that competition rules and fishing would be the last areas where compromise is found.
For Boris Johnson’s government, being tied to EU regulations in perpetuity defeats the purpose of Brexit and makes a mockery of “taking back control”.
For the European Union, it will not allow its internal market to be undermined by offering the UK unfair access.
Ursula von der Leyen has claimed the two sides have made a significant step by agreeing to a “strong mechanism” to ensure neither side lowers their environmental or social standards, but are yet to agree on how each could diverge from these levels in the future.
A good number of EU diplomats were quietly confident it was a matter of when, not if, EU access to UK fishing waters could be sorted. But it’s proving trickier than they thought.
Sources tell me that Michel Barnier explained to EU ambassadors at the start of this week that if fishing is resolved, then a wider deal would quickly fall into place.
But there’s no sign of a meeting of minds on fish, with the EU warning openly it may prove to be impossible.
But let’s remember this is the most intense of negotiations and that every public proclamation from London or Brussels will be chosen to strengthening their respective hands in what are the final days and hours of talks.
From the EU side, Mr Barnier said: “In this final stretch of talks, transparency and unity are important as ever.
“Good progress, but last stumbling blocks remain. We will only sign a deal protecting EU interests and principles.”
On Wednesday, European Commission President Ursula von der Leyen also said a “narrow path” had opened up for the two sides to conclude a deal.
What happens next with Brexit?
MPs are due to break up for Christmas later on Thursday, but Mr Gove confirmed they could be called back to the Commons if a deal is agreed between negotiators.
He said the government would “request that the House returns in order to make sure that we can legislate effectively”.
Although there is only 14 days until the deadline, Mr Gove also said he believed there was enough time for the necessary legislation to pass before 31 December “to give businesses legal certainty”.
But a number of opposition MPs raised issues already facing businesses waiting to discover the outcome of talks.
One Welsh MP, Jonathan Edwards, said: “I was contacted late last night by a businessman in my constituency who is reliant on imports from the continent and he can’t find a haulage firm willing to carriage on his behalf due to the current delays at the ports.
“He’s very concerned unless this issue was resolved his business would not survive into the new year.”
Mr Gove said he would get in touch with the business concerned.