Serena Williams, who has dropped to 172nd in the world after being sidelined for almost a year with injury and illness, has opted to use an injury-protected ranking to gain entry into the US Open, the United States Tennis Association said on Wednesday.

Champion Kim Clijsters will also be back to defend her title in New York after being sidelined during Wimbledon with a foot injury.

Williams, who won the last of her 13 grand slam titles at Wimbledon in 2010, can use her injury-protected No. 1 ranking to enter eight tournaments, including one grand slam, since she was sidelined over six months with health issues, according to the USTA. The American lost in the fourth round at Wimbledon last month after being out of action for nearly a year - during which she suffered a foot injury and life-threatening blood clots. The US Open runs from August 29 to September 11.