Naomi Osaka could be a doubt for the upcoming US Open after being forced to withdraw from the Canadian Open in the first round.
Osaka, up against Estonia's Kaia Kanepi, was playing in just her second tournament since Roland-Garros in May following a persistent Achilles injury.
But having come out on the wrong side of a tight first set to her opponent - during which she had a medical timeout to hint at her issue - Osaka then lost the first three games of the second set before telling the umpire at the change of ends that she could no longer carry on.
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The US Open in New York - the final major of the year - takes place from August 29 to September 11, giving the Japanese little time to correct the complaint.
Osaka had looked in decent enough fettle during the first set, even despite the problem that later became apparent.
She fought back from going down a break at 3-2 to level things up at 5-5 when Kanepi threw in a poor service game having appeared on the verge of taking the opener.
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A break of serve each followed, taking proceedings into a tie-break whereupon the 37-year-old Estonian took the last three points to wrap it up 7-4.
Osaka's body language - and level - were beginning to drop at the start of the second and when she went 3-0 down, it wasn't a huge surprise when she offered a handshake to her opponent.
"I felt my back from the start of the match," said Osaka. "And despite trying my best to push through it, I just wasn't able to today,"
Kanepi will go on to face Garbine Muguruza in the second round, with a potential third-round match-up with the retiring Serena Williams.
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