"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."
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)
