Dominic Thiem, the 2020 US Open champion, said Wednesday that he tested positive for COVID-19 after his first match in more than nine months.
Thiem lost 6-3, 6-4 to Pedro Cachin at the Andalucía Open on the lower-level Challenger Tour on Tuesday.
The 28-year-old Austrian had been sidelined by wrist and hand injuries and last competed in June.
Thiem posted on social media that he "started feeling unwell and didn't have a good night" after dinner Tuesday and developed what he called mild symptoms. He said he tested positive Wednesday.