"I am in bed with fever and there is almost no chance of a recovery until tonight... Of course I am disappointed, but nevertheless I had a solid start into the new season," the Austrian wrote on his official Facebook account.
The Australian Open men's field has already been hit by the withdrawals of five-times runner-up Andy Murray and Kei Nishikori. The participation of former champions Rafael Nadal, Novak Djokovic and Stan Wawrinka remains in doubt with the trio battling to overcome injury problems.
However, 24-year-old Thiem is confident he will swinging his racket come Jan. 15.
"Now I am focusing on Melbourne and being fit and prepared for the first grand slam of the year."
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Rublev, who beat Fernando Verdasco and Borna Coric in the previous rounds, came back from the brink of defeat to earn a 6-2 4-6 7-6(2) win over Argentine Guido Pella.
Monfils will be attempting to win the Doha event for the first time after finishing runner-up on three previous occasions.
(Reporting by Aditi Prakash in Bengaluru; Editing by David Goodman and Pritha Sarkar)
