WTA Champion Petra Kvitova has abandoned her title defence due to a viral illness, a day after losing her opener 6-4 6-1 to Agnieszka Radwanska.

The error-strewn, emotionally-fraught loss to the Pole in her opening group match had indicated there was something wrong with Kvitova’s fitness.

The champion finished tearful and angry both at her disappointing performance and that the scene of one of her finest triumphs had now become confusingly associated with such very different emotions.

It is a sad end to the 2012 WTA Tour for the left-handed Czech, who had emulated two achievements of her legendary compatriot Martina Navratilova by winning Wimbledon and becoming WTA Player of the Year in 2011, and had seemed capable of pushing on to become world number one.

Instead the ranking of two with which she started this year remains her highest.

The most her forthright flat-hitting style and refreshing willingness to attack the net has achieved since then has been semi-finals in the Australian and French Opens, while her ranking has slipped to six.

“I found out like 10 minutes before press that I wasn’t healthy with some virus, so I will find out tonight when I return to Prostejov what it really is,” Kvitova said.

“When I played I thought it was nerves, but normally nerves are gone after the first set. It went on all through the match, so then I thought there was something wrong. That’s why I have pulled out.

“After one rally with Agnieszka I couldn’t breathe, I was shaking all the match, and my stomach felt really funny. If I’m not a hundred per cent to compete with these girls at this level I know I can’t play.”

Kvotiva hopes to recover in time to play an exhibition with Maria Sharapova in the O2 arena in Prague on Monday, and to lead the Czech Republic’s defence of the Fed Cup in the final against Serbia at the same venue in Prague on November 3 and 4.

Her departure gave Australia’s Samantha Stosur a last-minute call-up to play in the championships.

The former US Open champion can still qualify for Saturday’s semi-finals if she wins the remaining two matches in the white group, against Sharapova, the second seed, and Sara Errani, the French Open runner-up.