Luxembourg’s prime minister was admitted to hospital on Sunday after testing positive for coronavirus a week ago.
Xavier Bettel will have “supplementary tests and analysis” as a “precaution” and is set to stay under observation for 24 hours, said a statement from the country’s government.
Mr Bettel tested positive on 27 June and was suffering only mild symptoms such as fever and headache as he entered a 10-day period of self isolation.
The 48-year-old’s diagnosis came two days after he had attended a European Council summit with other EU leaders in Brussels.
Mr Bettel has been head of the tiny – but very wealthy – state of just over 600,000 people since 2013.
Other world leaders who have had the disease include France’s Emmanuel Macron, Brazil’s Jair Bolsonaro and UK Prime Minister Boris Johnson.