Perth, Jan 6: World No.1 women\'s tennis player Serena Williams announced her withdrawal from the Hopman Cup because of an injury in the left knee on Wednesday.

The Hopman Cup is an annual tournament held here between mixed-gender teams held on a country-by-country basis, reports Efe.

Serena\'s injury forced her to miss out on the United States\' first match in the tournament against Ukraine, while her condition worsened during her match against the Australian Jarmila Wolfe on Tuesday.

Williams withdrew from the match while down 5-7, 1-2, and said after the match she was suffering from a small inflammation in the left knee and needs some time to recover.

Despite not ruling out that she will play again on Thursday, the organising committee of the tournament confirmed her withdrawal. She will be replaced by Vicky Duval in the final clash against the Czech Republic.

The injury is a concern for Williams with less than two weeks to go until she begins the defence of her Australian Open title, the season\'s first Grand Slam.

Injured Serena Williams withdraws from Hopman Cup