Mr Barnier will brief officials from the EU27 on an apparent list of lingering issues stalling the resolution of Britain’s official departure from Brussels.
On the list is the Northern Ireland border riddle as well as a framework on the UK’s future relationship with the EU post-Brexit.
The meeting in Brussels follows the publication of Britain’s post-Brexit immigration rules in a report issued by the Migration Advisory Committee (MAC).
The report will be further discussed at a crunch summit of member state leaders to take place tomorrow in the Austrian city of Salzburg, which will see Prime Minister Theresa May plead for her counterparts to back her controversial Chequers plot.
The plan, which could see Britain remain shackled to the EU’s single market and customs union, is being pushed by Mrs May who attempted to garner support from another Prime Minister ahead of the summit.
Mrs May hosted Malta’s Prime Minster Joseph Muscat at No 10 this week and gave him a sneak peak at her proposal before showing it to leaders of the other member states.
A Downing Street spokesman said the two “discussed the Chequers proposal and the importance of achieving a mutually beneficial economic and security partnership”.
Mr Barnier also met with EU leaders in the run-up to the Salzburg summit, having met with Spanish Prime Minister Pedro Sanchez, who offered “full support” Madrid’s argument to include Gibraltar in Brexit negotiations.
Mr Sanchez said the guarantee on the small British territory needed to be concluded “ASAP”.
Mr Barnier also insisted any declaration agreed by Mrs May on future relations wth the EU would not be picked apart by whoever fills her shoes as Britain’s next prime minister, according to The Times.
Despite environment secretary Michael Gove calling Mrs May’s Chequers plan the “right one for now”, it has been the subject of controversy among her warring cabinet.
This could see Mrs May ousted in a leadership challenge at the coming Conservative Party conference on September 30.
Contenders include Boris Johnson who spearheaded much of the Leave campaign with tireless arguments on how the billions Britain showered the EU with could be better spent on funding the crumbling NHS.
Home secretary Savid Javid is also said to be in the running as well as defence secretary Gavin Williamson.
There are also talks foreign secretary Jeremy Hunt has his eyes on the prize.