World number one Serena Williams says a knee injury has forced her to pull out of this week’s BNP Paribas Open at Indian Wells. Williams, 35, said she will also miss the Miami Open later this month. The American, who won an Open era record 23rd Grand Slam at the Australian Open earlier this year, said: “I have not been able to train due to my knees.” She added she would return “as soon as I can”. Indian Wells organisers said a revised draw would be issued later. Williams only returned to the Californian tournament in 2015 after a 14-year boycott following claims she had suffered racist abuse at the venue. Her withdrawal means Germany’s Angelique Kerber is set to replace her as world number one.