Melbourne - Stefanos Tsitsipas said he was left coughing and had trouble breathing even after practising indoors at the Australian Open, where the build-up has been dominated by fears about toxic smoke from bushfires.
The Greek world number six, a major contender for the first Grand Slam of the year, said on Saturday that he had been excited about coming to Melbourne - until he saw "smoke over the city" as his plane came in to land.
"I was like, 'What is this?'" said the 21-year-old, who stunned Roger Federer last year en route to the Australian Open semi-finals.
"First two days here were pretty unusual... I went to practice for around one, one-and-a-half hours.
"After I practised indoors I felt really bad with my lungs."
Tsitsipas, who capped a breakthrough 2019 by winning the season-ending ATP Finals, added: "I'm feeling okay now, but I was a bit concerned.
"I was coughing a lot had troubles breathing for a couple of hours."
Air quality in Melbourne was among the worst on the planet on Tuesday and Wednesday, and Australian Open organisers were strongly criticised for pushing ahead with qualifying matches.
On Saturday, two days before the main draw begins, air quality in the city was rated 'moderate'.
Rain is forecast on Monday - which should help clear the air - and Tsitsipas hopes there will be no repeat of the discomfort he felt.
"It's getting better day by day. I had a practice session today as well," he said.
"It's much different than it was when I first came."