Luxembourg's prime minister Xavier Bettel is in a "serious, but stable" condition in hospital with Covid-19 a week since first being diagnosed with the illness, the government said in a statement.
The running of state affairs has temporarily been handed over to finance minister Pierre Gramegna for now, with Mr Bettel expected to remain in hospital for up to four more days.
The 48-year-old prime minister had an insufficient level of oxygen saturation, as well as coughing and fever, and was taken into hospital for tests on Sunday.
“The medical state of the prime minister is considered serious, but stable,” the government statement said. A source told AFP that Mr Bettel “is short of breath, but not intubated”.
Mr Bettel had received one shot of the AstraZeneca vaccine and had been due to receive his second last week but tested positive for the illness just before receiving it.
A member of the centre to centre-right Democratic Party, Mr Bettel became one of the world’s first openly gay heads of government when he took up the office in 2013.
He was centre stage at the European Council meeting in Brussels 10 days ago at which the 27 leaders confronted Hungary's Viktor Orban over a discriminatory anti-LGBT law.
Dutch prime minister Mark Rutte described the leaders has having “tears in their eyes” after Mr Bettel spoke of his own struggle to come out and the risk that the Hungarian law posed to young gay people.
Two days after the summit ended, he tested positive for Covid-19. A spokesman for the European Council said that “all sanitary measures were in place” for the summit and that Mr Bettel had tested negative before attending. No other leader has tested positive since the Council took place.
European Commission president Ursula von der Leyen wished Mr Bettel “a very speedy recovery” in a message on Twitter. “Hope to see you soon in good health. In the meantime, rest and take good care of yourself,” she wrote.