Mr Barnier was due to give an update on Brexit negotiations at a press conference in Luxembourg at 7:30 UK time (8:30pm local time).
But the Frenchman’s appearance in front of the press was called off around an hour later.
EU sources told Express.co.uk that Mr Barnier was stuck in an meeting of the EU’s General Affairs Council (GAC) which was over-running.
The GAC, made up of the EU27’s foreign ministers, was holding talks to discuss the key issues surrounding Brexit.
The officials talked about the future of the Northern Ireland border, as well as the UK’s post-Brexit trading arrangements with Europe.
They also discussed the prospect of bringing Article 7 proceedings against Poland to strip the nation of its EU voting rights.
Mr Barnier’s snub to the media comes ahead of Thursday’s EU summit in Brussels, as the UK tries to resolve the deadlock in divorce negotations.
However, the meeting is likely to be overshadowed by other issues as EU leaders discuss the migrant crisis, security and the bloc’s finances.
One Brussels insider described the UK’s impending divorce from the bloc as a mere “footnote” at the bottom of the summit’s agenda.
Earlier today, the Queen granted royal assent to Theresa May’s flagship Brexit legislation, the EU Withdrawal Bill.
Cheers erupted in the House of Commons as Speaker John Bercow announced the bill had been signed into law by the monarch.
The bill, which enables EU law to be transferred into UK law, was subject to fierce parliamentary debate in the Commons and Lords.
The Lords, where the Government does not have a majority, made 15 key changes to the legislation, which were later overturned by MPs.
Meanwhile, Mrs May distanced herself from Brexiteer Boris Johnson over his reportedly expletive-fuelled outburst against business leaders.
The Foreign Secretary is said to have exclaimed “f*** business” when asked about the Brexit fears of some company bosses.
The Prime Minister declined to say if she had reprimanded him over the comments, but said the Government would “listen to the voice of business”.
She added: “Business is at the heart of how we are going to develop this country.
“We want to ensure we are listening to the business voice because business provides the backbone of our economy.”