Defending women's champion Petra Kvitova and tournament's second seed Agnieszka Radwanska withdrew from this month's Australian Open on Sunday. They are the latest tennis stars to pull out of the competition.

Kvitova, currently the world's No.6 and the third seed of the tournament, will not be able to defend her Sydney title after yielding to a gastrointestinal illness, which afflicted her during the Shenzhen Open in China last week.

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"I'm really disappointed to have to withdraw from the Sydney International but unfortunately I am still not feeling well," Kvitova said.

It is the second consecutive event from which the world number six has withdrawn in 2016. She retired with a stomach virus during the first round of the Shenzhen Open.

Kvitova has won 17 career singles titles including two Grand Slam titles at Wimbledon. She reached her career-high ranking of world No. 2 on October 31, 2011. She is the current Czech number 1 and highest-ranked left-handed player in the WTA.

Radwanska of Poland, who is fresh from winning her 18^th WTA Tour title in the Shenzhen Open, joined the Czech ace after pulling out of the Sydney competition with a left leg injury.

The Pole produced very impressive performances at the end of the last season campaign winning several titles in Tokyo, Tianjin and the WTA Finals in Singapore. Radwanska is set to go up to be the World's No. 4 in the latest WTA ranking, replacing Maria Sharapova of Russia.

Radwanska said she needed to rest her leg after playing five matches in the past week.

"I'm really sorry that I can't play in Sydney this week. I am feeling very confident in my game at the moment and the results are there, but after five matches in the past week my leg needs some recovery time," she said.

Top ranked stars Serena Williams, Simona Halep,Garbine Muguruza And Maria Sharapova have also withdrawn from the tournament due to injuries.

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