Juncker to critics: 'I'm not tired or sick'

Juncker had come under fire in recent weeks, in press articles as well as from politicians and diplomats in different countries, over his work style, leadership qualities, his smoking and drinking habits and his general comportment.

He has also faced calls for his resignation over the Brexit fiasco and his handling of the fallout of the UK vote.

Estonian president Toomas Ilves said Juncker’s behaviour had been “abominable”.

Czech foreign minister Lubomir Zaoralek said he was not "the right man for the job”.

Polish ruling party chief Jaroslaw Kaczynski said “the whole European Commission in its current composition” should take responsibility for the UK exit.

Juncker’s decision to speak publicly about his own health amounted to a rebuttal of speculation that he would leave office before his mandate ended in 2019.

"Juncker will not resign," a senior source from one EU state told a group of journalists in Brussels the same day.

"Attacks come from the usual media and from only a few people with grudges against the commission, it's not a trend," a commission official told EUobserver.

The critics are not easily stopped however.

Some member states, particularly in eastern Europe, are still angered by how the commission and its chief have handled the migration crisis, particularly by pressing for mandatory quotas to distribute refugees across the continent.

Juncker and his commission had spearheaded German-inspired policies during the crisis.

But for some EU states, the Berlin-Brussels axis should not become a permanent fixture.

“The commission will have to change, quit the habits that it has developed over the last two years, like running ahead, no matter what, without consulting the member states," an EU diplomat said.

“There are plenty of examples of the commission just 'not getting it’, from the migration crisis on, the list is very long," he added.

Another member state source said Juncker’s commission is begging to be seen as “part of the problem” also in Berlin.

Even inside the commission, critics can be heard.

"His reaction to the outcome of the [UK] referendum [on Friday] was dramatic," a source told EUobserver.

"He talked three hours after [EU Council president Donald] Tusk, he was not in his best shape, he read a statement and answered only two questions before running off."

Despite the criticism, there is no ploy afoot to unseat the Luxembourgish politician.

"I don’t have the feeling that there is any kind of movement in the [EU] Council against Juncker," an EU diplomat said.

He added that Juncker’s departure could trigger an EU institutional crisis on top of the bloc’s other problems.

Another source said the commission could not be decapitated at a time when serious negotiations with the UK were about to get under way.

“Nobody can push him out, unless there was serious ground," the commission official said.