Dominic Thiem, the 2020 US Open champion, has 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 Andalucia Open on the second-tier 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 and developed what he called mild symptoms. He said he tested positive on Wednesday.
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Thiem was the runner-up at the French Open in 2018 and 2019, losing to Rafael Nadal each time, and at the Australian Open in 2020, losing to Novak Djokovic.
Later that year, he fought back from two sets down to beat Alexander Zverev in a fifth-set tiebreaker in the US final.
Once ranked as high as No.3, Thiem is currently No.50.