The 'Careless Whisper' singer was meant to play in Strasbourg, France tonight, as well as in Cardiff on both Saturday and Sunday night, but all three gigs have been postponed.
His spokeswoman confirmed that he is receiving treatment for the illness, stating that rescheduled dates "will be provided when available".
Michael was hospitalised in Vienna, Austria, where he was due to perform on Monday.
His concert promoter Manfred Leodolter told Austrian reporters: "George Michael is still in Vienna. Doctors have warned him for the moment against flying and he is getting rest in Vienna."
The 48-year-old missed an earlier date of his UK Symphonica orchestral tour last month after suffering from a 'viral infection'.
Watch the video for George Michael's 'Careless Whisper' below: