Serena says she'll make Aussie Open

Reigning champ battling troubling knee problem

Serena Williams' preparations for the Australian Open took a potentially significant blow when she was forced to retire with a knee injury during the United States' 3-0 Hopman Cup loss to Australia Gold on Tuesday evening.

The world No 1 retired due to soreness in her left knee during her singles match against Jarmila Wolfe, trailing 7-5, 2-1.