PERTH, Australia (AP) -- Serena Williams withdrew from the Hopman Cup on Wednesday because of inflammation in her left knee, a setback in her preparations for the Australian Open.
Williams has been replaced by Vicky Duval in the U.S. team for the last Group A match against the Czech Republic on Thursday. Williams withdrew ahead of her season-opening match against Ukraine on Monday, with Duval filling in for her, and retired in the second set against Australia's Jarmila Wolfe on Tuesday.
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Hopman Cup organizers confirmed Williams' withdrawal on Wednesday. The U.S. team is 0-2 and cannot reach the final of the international mixed team competition at Perth Arena.
Williams, who won the Australian Open, French Open and Wimbledon and got within two victories of a season Grand Slam in 2015 before losing in the U.S. Open semifinals, had initially been confident of returning to action in Perth.
"It's not even a bump - just a really minor thing in the road and I'll fly over it," Williams said after retiring against Wolfe. "I just have some inflammation that's been going away very slowly - it's going away but it needs a little more time.
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"Mainly I was afraid to move and I need to get in the space where I'm not afraid to move. Maybe a day off or two will really make the world of difference."
Williams is expected to travel to Melbourne to continue preparations for the Australian Open, which begins on Jan. 18.