Defending champion Victoria Azarenka was forced to withdraw on Tuesday from the women’s event at the ATP-WTA Cincinnati Masters with a right knee injury, AFP reports.

Officials replaced her in the draw with German Mona Barthel who plays

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Due to a foot injury Azarenka, owner of two Australian Open titles, has played just six events in 2014. Her best showings were quarter-finals in Melbourne and last week in Montreal.

“After my last match in Montreal, I tried to recover as much as possible. I started to feel a little bit better and did everything I could, but it’s just not enough time for me to feel good to play a full match,” said Azarenka.

“I tried to practise, give it a rest and work with my team. It’s just not enough time. I wanted to give it my best shot until the last moment and try to do the best job as possible.

“It’s unfortunate but it’s the best decision for me.”