Kyrgios is struggling to digest his third-round exit after being forced to retire mid-match against Illya Marchenko because of a hip flexor injury.
The defeat ended his record of never having lost to an unseeded opponent in 14 grand slam appearances and denied the 21-year-old a fourth-round shot at former Australian and French Open champion Stan Wawrinka.
“This one hurts man,” Kyrgios posted in Twitter.
“My sights were set on some great things this week … Not the way I wanted to end the last grand slam of the year. F**king sucks. #liveandlearn. Its only a failure if you don’t learn the lesson.
“Goodluck to everyone still going.”
Not the way I wanted to end the last grand slam of the year. F**king sucks. #liveandlearn https://t.co/d8JeoVm682
— Nicholas Kyrgios (@NickKyrgios) September 4, 2016
Kyrgios’s Open ended in tears, Australia’s world No.16 unable to contain his emotions in front of a packed Saturday night crowd at Arthur Ashe Stadium.
Yet McEnroe harshly challenged the two-time grand slam quarter-finalist to quit the game if his heart wasn’t in it.
“Nick Kyrgios, if you don’t want to be a professional tennis player, do something else,” McEnroe said while commentating on US TV.
“He’s hurt because he’s not training enough.”
Kyrgios, though, attributed the injury to training overload before the tournament as he sought to find his best form for the season’s final slam.
The setback also forced Kyrgios to officially withdraw from the US Open doubles after he’d charged into the last 16 with British partner Dan Evans.
The injury has also cast doubt over Kyrgios’s availability for Australia’s Davis Cup playoff with Slovakia in Sydney from September 16-18.
He was in no mood to discuss Davis Cup in the immediate aftermath of his Open exit.
“I don’t really care right now, to be honest,” Kyrgios said.
“Hopefully I get better in time. Obviously I want to play but I’m not really thinking about that right now.”
Australian captain Lleyton Hewitt is due to name his team on Wednesday.
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