Alexander Zverev said his energy began to fade midway through his five-sets Australian Open semifinal loss to Daniil Medvedev on Friday and blamed an illness following his win over Carlos Alcaraz in the last round.
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Zverev was two points from a win after going up 5-4 in the fourth set tiebreak before crashing to a 5-7 3-6 7-6(4) 7-6(5) 6-3 defeat but the German said his issues began earlier.
"End of the second set I started to lose energy. I started to not feel so fresh anymore," Zverev told reporters.
"I got a bit sick after the Alcaraz match with a bit of fever so that didn't help the recovery and I did play quite a lot.
"Against him (Medvedev), it's impossible to play when you're not 100% physically, because he's literally someone that really doesn't give you anything.
"He makes you work for every single point and once you can't really do that anymore, it becomes difficult. I was close in the third and fourth sets, but I wasn't the same player as I was the first two sets anymore. I was just hanging on."
There were many frustrating moments for Zverev during the match, including one where he smashed the net with his racket at 2-2 in the decider after missing a volley.
He was also asked about his defeat from two sets up in the 2020 US Open final by Dominic Thiem, but said Friday's loss was different.
"It's more frustrating that I didn't feel 100% physically. It took the chance away," Zverev said. "I lost it because of a physical state, not because of tennis."
Zverev said an upcoming court case in Germany on physical abuse charges had not affected his concentration.
The 26-year-old, who rejects the allegations, is due to appear before a Berlin court on May 31 on charges of abusing his former girlfriend.
"I have said it before: Anyone who has a semi-decent IQ level understands what's going on," Zverev said. "I hope that most of you guys do. I'm fine with it."