Serena Williams pulls out of Hopman Cup due to injury

World Number One Serena Williams is out of the Hopman Cup in Perth, Australia due to a knee injury. She was due to play her first official match for the U.S. team but pulled out after her knee became inflamed during a morning warm-up session. Williams was using the event as preparation for her 22nd grand slam singles title campaign at the Australian Open later this month. She will be replaced in the U.S. team by 20-year-old Vicky Duval.