Dominic Thiem suffered a 6-3, 3-6, 6-4 loss to John Millman in the opening round of the Serbia Open on Tuesday in his first tour-level match in 10 months.
The 2020 US Open champion and former World No 3 had been sidelined with a wrist injury suffered in a grass court tournament in Marbella in June last year.
The 28-year-old Austrian returned to action in the same Spanish city last month in a second-tier Challenger clay court event where he lost in the first round. He tested positive for Covid-19 the day after that defeat.
Thiem, a two-time French Open runner-up and 2020 Australian Open finalist, has slumped to 54 in the world during his prolonged absence.
Buy an annual Scroll Membership to support independent journalism and get special benefits.
Our journalism is for everyone. But you can get special privileges by buying an annual Scroll Membership. Sign up today!