Dominic Thiem withdrew from a scheduled match at the Kooyong Classic on Thursday as he recovers from a virus, disrupting the world number five's build-up to the Australian Open.
The Austrian played at the Grand Slam tune-up event on Wednesday, losing in straight sets to Novak Djokovic.
He had arrived late in Melbourne from Doha after pulling out prior to last weekend's Qatar Open semi-final with Gael Monfils after contracting a virus.
Thiem was bed-ridden before flying to Australia, but said after facing Djokovic that he felt fine and was over his illness.
"I'm free of fever and healthy again," he insisted then.
He has been replaced at Kooyong by Russian rising star Andrey Rublev, the losing finalist in Doha to Monfils.