From the official site:
With great regret, George Michael has been forced to postpone his November 21 concert at the Stadthalle, Vienna.
A doctor visited George this afternoon and confirmed he is suffering from a chest infection, and on medical advice he has been advised that he cannot perform tonight to allow him time to recover before his next concert at the Zenith, Strasbourg, on Wednesday, November 23.
A spokesman for George Michael said that “he is disappointed that he cannot perform tonight’s concert, but he has been advised to rest, and is very sorry that he has had to postpone”.
The promoters have asked ticket holders for tonight’s concert to retain their tickets. Further announcements regarding a replacement date will follow.
All other dates on Symphonica – The Orchestral Tour will not be affected.
The tour commenced in late August. George has performed 45 shows to date as part of his Symphonica – The Orchestral Tour.