George Michael is in hospital suffering from pneumonia, his publicist said tonight.
The singer was due to appear in Vienna as part of his Symphonica tour on Monday but cancelled two hours before the concert was due to start.
Connie Filippello said in a statement that the 48-year-old has been “diagnosed with pneumonia and he is currently receiving treatment”.
Austria’s state broadcaster reported that he is being treated in Vienna’s AKH hospital.
Ms Filippello said further dates in Strasbourg and Cardiff would now be rescheduled. Michael was due to appear at Cardiff's Motorpoint Arena this weekend.
She added that new dates “will be provided when available”.
Earlier this month, the star played a special gig at the Royal Opera House in London which raised money for Elton John’s Aids Foundation.
A star-studded audience including Elton, David Walliams, Kylie Minogue and James Corden were at the show in which the former Wham! singer was accompanied by a symphony orchestra.