The 22-year-old suffered a straight-sets defeat by Agnieszka Radwanska, with the 2011 Wimbledon champion later revealing she felt sick throughout the match.
“On Tuesday, when I played I thought I was nervous, but normally nerves are gone after the first set, and it was actually happening during all the match,” said Kvitova.
“I was shaking all match and wasn’t feeling very well. My stomach felt funny. After one rally with Agnieszka I couldn’t breathe. So I thought there was probably something wrong.”
The Czech Republic No1 revealed it was the first time she has pulled out of a tournament in her short career to date, with Sam Stosur replacing Kvitova.
“I’m really sad to withdraw from the tournament,” Kvitova added. “It’s a great tournament and it was an honour to be here.
“I hope I can come back next year again. I’ve never withdrawn from a tournament, this is the first time for me. I don’t like to give up, so I’m really disappointed.
“I hope that Sam will win some matches for me.”
Stosur lost to Caroline Wozniacki in the Kremlin Cup final on Sunday and the Australian, who faces Sara Errani on Thursday, is relishing the chance to play at the season-ending event.
“I came to Istanbul straight from Moscow where I played on Sunday, so I got here late, so obviously it is a little bit strange to come here straight after playing a tournament as an alternate and now get a chance to play in the WTA Championships,” said Stosur.
“But this is my third time playing this event and I’m really happy to be in Istanbul.”
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