19 January 2014 Last updated at 12:12

Australian Open: Serena Williams discusses back injury

Serena Williams says she should "probably" have pulled out of her fourth round Australian Open defeat by Ana Ivanovic with a back injury.

The world number one reveals she has been struggling with the problem for a "few days" and can play "ten times better" than she did in Melbourne.

Former world number one and 2008 French Open champion Ivanovic fought back from a set down to win 4-6 6-3 6-3 - her first ever victory over Williams in five attempts.