PERTH, Australia — Serena Williams withdrew from her opening match at the Hopman Cup due to a knee problem, an early setback in preparations for her Australian Open title defense.
No. 1-ranked Williams practiced on Monday ahead of her scheduled season-opener for the US team against Elina Svitolina of Ukraine in the international mixed team competition at Perth Arena, but withdrew from the match citing knee inflammation.
Vicky Duval filled in for Williams in the Group A match, losing, 6-4, 6-1, to Svitolina in the first singles match and giving Ukraine a 1-0 lead in the best-of-three match round-robin encounter.
Williams said she was confident she'd be able to join Jack Sock in the US team to play the Australia Gold team on Tuesday.
After winning the Australia, French and Wimbledon titles in 2015 Williams had two months off after the US Open, where she narrowly missed completing a season Grand Slam by losing to Roberta Vinci in the semifinals.
The 20-year-old Duval returned to tennis in August after overcoming Hodgkin's lymphoma.