Victoria Azarenka forced to pull out of Madrid Open with lower back injury

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Women's world No 5 Victoria Azarenka has withdrawn from the Madrid Open due to a lower back injury.

The two-time Australian Open champion was set to meet American Louisa Chirico in the third round but the latter has now been given a walkover.

Azarenka had seen off Britain's Laura Robson and then France's Alize Cornet in previous rounds.

Victoria Azarenka plays a forehand during her second-round victory against Alize Cornet on Monday

Azarenka (right) shakes hands with Great Britain's Laura Robson after their first-round match in Madrid

Azarenka said 'I don't feel that I'm able to compete today' and added that she will undergo medical tests in Madrid later on Wednesday before making a decision about playing in Rome.

She says it is going to be a matter of making the 'smart decision.'

The fourth seed's withdrawal is the latest big name exit at the Madrid Open, with top seed Agnieszka Radwanska, current Australian Open champion and second seed Angelique Kerber and third seed Garbine Muguruza all leaving in previous rounds.

Petra Kvitova, the fifth seed, also exited on Wednesday, losing 6-3, 6-4 to Australia's Daria Gavrilova.

Australian Daria Gavrilova plays a backhand during her match against Petra Kvitova on Wednesday

Kvitova (right) congratulates Gavrilova across the net after the Czech fifth seed was knocked out