George Michael has been forced to postpone the rest of his "Symphonica" tour as he battles pneumonia in Vienna hospital, his agent said on Friday.
The 48-year-old British singer was said to be responding to treatment and "slowly improving", but has been ordered to rest.
Concerts in Vienna and the French city of Strasbourg were called off and 14 dates in Britain, including three in London, have now been postponed.
"While George is receiving excellent medical care and is responding to treatment and slowly improving, to ensure his complete well-being, George's doctors have advised that he cannot perform the rest of his 'Symphonica' tour and that he instead takes a full and complete rest," said a statement on his website.
It said discussions were under way to reschedule dates and advised ticket holders to retain their tickets.
The "Careless Whispers" star, who found fame in the 1980s pop duo Wham! and has gone on to sell more than 100 million records worldwide, spent a month in prison last year for driving under the influence of drugs.
He has performed around 45 shows to date as part of his "Symphonica -- The Orchestral Tour" that began in August, winning critical acclaim.