Tournament director Rod Leembruggen said Bjorn did not give a reason for his withdrawal.
'It's a shame to lose Thomas,'' Leembruggen said. 'He is a previous winner and seemed to be in good form early in the season.
'I haven't spoken to Thomas yet about why he won't be here, but he has been such a loyal supporter over so many years that we can certainly accept one miss.''
The tournament, which features Ernie Els, Greg Norman and Stuart Appleby, begins Thursday at Royal Melbourne.
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