Stefanos Tsitsipas admits is 'something missing from his game,' although he says the absence of fans affected him at the O2.
Tsitsipas is the defending champion at the ATP Finals, but he lost his opening match this year to Dominic Thiem.
He offers no excuses for that, although he does say he missed the energy of fans inside the arena.
“There is something missing from my game and I have to fix it or work on it," Tsitsipas said.
"But the atmosphere makes it tougher. I am a person that feels the energy of the crowd and I have won many matches because of the support."
Tsitsipas arrived in London after struggling with a leg injury, but he says he is just about over that now and, at least relatively, pain-free.
“I’m happy that I’m able to move more freely and less conscious of my pain.
"So it’s a positive feedback, and a positive thing to have, [because] this injury kind of mentally drained me.
“I was not quite sure if it’s the right thing to do, to keep playing, but I proved that the mind can do anything if you set yourself a goal and you want to pursue it.
"Right now, I’m feeling way, way better than I did in Vienna. I hope my leg stays the same.”
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