The 64-year-old former Luxembourg prime minister was forced to cut short his summer holiday to undergo surgery in his home country this weekend and doctors have advised him not to travel.

It means Juncker, the European Commission chief, will miss the chance to meet Boris Johnson for the first time since he became British prime minister, as fears grow that Britain will crash out of the bloc without a divorce deal on October 31.

"President Juncker had to shorten his holiday in Austria for medial reasons. He was taken back to Luxembourg where he was to undergo an urgent surgical removal of the gall bladder," commission spokeswoman Natasha Bertaud told reporters.

"That surgery took place during the weekend. The surgery went well and President Juncker currently remains in hospital in recovery. His doctors have specified that he should not travel at this time and we are therefore also able to confirm that he will not be able to attend this weekend's G7 meeting."

Juncker will discuss plans for EU representation at the G7 meeting in the southwestern French town of Biarritz with host President Emmanuel Macron and EU Council President Donald Tusk, she added.