Serena Williams is going to rest her back for the Olympics.

Williams won her fifth Wimbledon title this month and eight days later captured the Bank of the West Classic in California. Olympic tennis begins July 28 at Wimbledon.

She said Friday she was pulling out of a World Team Tennis match for the Washington Kastles on Sunday. She'll be replaced by sister Venus.

Serena Williams says she needs to rest her back after her two recent victories, adding: "I'm disappointed that I won't be able to see my D.C. fans, but can't wait to go for gold in London."

Williams is the favorite in London and has never won an Olympics singles title.

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