Williams has not played since she won the 2017 Australian Open title, but a problem with her left knee has forced the 35-year-old to pull herself out of the event at the Indian Wells Tennis Garden.

Germany's Angelique Kerber will now reclaim the number one spot from the American, who needed to reach the semi-finals in Indian Wells to retain the ranking she claimed following her win in Melbourne.

Williams has not won this event since 2001 largely because she refused to play for the subsequent 13 years after being booed during the victory ceremony after her elder sister Venus had withdrawn before they were due to meet in the semi-final.

In today's action, Italy's Francesca Schiavone secured her place in the main draw of the women's singles competition after she defeated Elitsa Kostova of Bulgaria today.

The 36-year-old, who won the French Open title in 2010 and has reached the quarter-finals of the other three major tennis tournaments, fell behind after Kostova eased into the lead by taking the opening set 6-1.

Kostova, currently 136th in the world, failed to maintain that level of performance as Schiavone came back to level the match, winning the second set 6-0.

By that stage the Italian had taken full control and coasted to victory after taking the third set 6-0 also.

Varvara Lepchenko of the US also secured her place in the main draw, much to the delight of the home crowd.

The 30-year-old, ranked 51 in the world, overcame Lucie Hradecka of the Czech Republic 6-3, 6-0.

Denis Istomin of Uzbekistan, who shocked Novak Djokovic in the second round of the 2017 Australian Open, was forced to retire in the first qualifying round of the men's singles event today.

It was Djokovic's earliest exit from a grand slam since his second round loss at the Wimbledon in 2008, but Istomin could not maintain that form as he chose to end his match prematurely.

The 30-year-old lost the opening set to the US' Dennis Novikov 7-6 but, with the score at 4-2 to his opponent in the second, Istomin brought the match to an end.

Latvia's Ernests Gulbis was also knocked out today after he was beaten in straight sets by Kazakhstan's Alexander Bublik

Gulbis, who reached the semi-finals of the 2014 French Open, lost 4-6, 6-7 to Bublik, currently ranked 138 in the world.

Julien Benneteau of France was victorious today as he defeated Australia's Sam Groth 6-4, 7-6.

Tobias Kamke got the better of Benjamin Becker in an all-German clash.

Becker, who reached round two of last year's Wimbledon competition, fell behind as Kamke took the opening set 7-5.

The match was then taken to a decider when Becker edged the second 6-3 before Kamke moved within one match of reaching the main draw when he won the third and decisive set 6-4.

Main draw action starts in the women's competition tomorrow alongside the men's second qualification round.