Washington - Australia's 17th-ranked Nick Kyrgios withdrew from the ATP Washington Open on Wednesday because of a hip injury.
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The 23-year-old from Canberra, who won his fourth career ATP title in January at Brisbane, retired last week from a quarter-final at the Atlanta Open due to the hip injury.
"Absolutely gutted to have to withdraw from @CitiOpen," Kyrgios tweeted. "I've done all I can to get my hip ready but ran out of time. I want to thank Keely (O'Brien, tournament director) & her team for the support and apologise to the fans. I'll be back!"
Kyrgios, who had a first-round bye as the fifth seed, was replaced by 105th-ranked qualifying lucky loser Jason Kubler for a Wednesday match against fellow Australian James Duckworth.
Kyrgios reached the third round last month at Wimbledon after semi-final runs at Stuttgart and Queen's.
The injury raises doubts about whether Kyrgios will be ready for the US Open, which starts August 27 in New York.