Novak Djokovic revealed he was suffering from dizziness and sickness towards the end of his surprise Serbia Open defeat to Aslan Karatsev.
Djokovic and Karatsev played out a memorable epic, battling each other for nearly three-and-a-half hours before the Russian won 7-5, 4-6, 6-4.
After the match, Djokovic revealed he was suffering some health problems in the third set, although he was keen to stress it should take nothing away from Karatsev.
"He played fast, the way he knows," Djokovic said. "I expected it.
"I started well, but there were many different factors. Decreased concentration, physical fitness and health.
"In that third set, I played most of the time with dizziness. I was really sick, and I had an opponent who pressed me. He was phenomenal, he played accurately. Congratulations to him. He won in the best way."
Djokovic was also asked what was missing from his performance, but he said it was difficult to say right now.
"I don't know, maybe a little luck," he said. "Probably if I analysed the whole match to know more, it all came down to a shot or two.
"That decides the winner at this level. It's a sport, sometimes it prevails on your side, sometimes not.
"I fought but the level of play on my part was pretty bad I keep working I'm sorry I lost."
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