Tennis star Novak Djokovic alluded to a health condition after an early exit from the Cincinnati Open on Saturday, in which he lost to 25-year-old Thiago Agustín Tirante in the second round.

Djokovic, 39, was visibly struggling throughout the match and appeared to vomit at one point, requiring a medical timeout. The match lasted nearly three hours before Tirante ultimately took down the 24-time Grand Slam champion.

It was “not an enjoyable” match, Djokovic told reporters after the loss.

“It’s just a condition that I have, healthwise, that has been bothering me for the past couple of years,” Djokovic said. “A lot of issues, especially when it is humid and it is hot.”

The Serbian star did not name or elaborate on the health issue. He had anticipated the humidity heading into the match but noted that other factors, including nerves, “make it worse.”

Djokovic congratulated Tirante after the match. Tirante, for his part, called the win potentially the best of his career and praised Djokovic as one of the most important figures the sport has ever seen.

“I think I really did a good job inside the court,” Tirante said. “I managed very well the nerves of playing against a legend like Novak.”

Djokovic saved 13 of the 15 break points he faced, but Tirante broke his serve in the ninth game of the final set and served out the match, winning 2-6, 6-4, 6-4 in 2 hours and 44 minutes.

Djokovic has long dominated at the Cincinnati Open, but Saturday’s loss dropped his record there to 45-13, according to the ATP Tour — and it may be his last appearance at the tournament.

Asked whether he’d return, Djokovic seemed uncertain.

“I certainly hope so, but it looks more likely not, unfortunately,” he said. “But let’s see what the future brings.”

This tournament was Djokovic’s first since his loss to Italy’s Jannik Sinner at Wimbledon in July.

He withdrew from the Canadian Open earlier this month, likely resting up ahead of the U.S. Open — the year’s final Grand Slam, which begins Aug. 30. Djokovic has won the title four times.