Former World No. 1 Pat Rafter says Nick Kyrgios can be the best

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      Nick Kyrgios 'can be world No. 1'

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    Nick Kyrgios 'can be world No. 1' 00:49

    Story highlights

    • Rafter says Kyrgios needs mental preparation
    • World No. 13 Kyrgios can win Wimbledon says Rafter
    • Kyrgios still competing without a coach

    London (CNN)Australian tennis bad boy Nick Kyrgios has what it takes to be world No. 1, according to a man who reached the top of the sport.

    Pat Rafter, a two-time Wimbledon finalist, also backed his compatriot to one day win the grass court grand slam.
      "I know that talent-wise, he's as good as I have seen in the last 20 years," the twice US Open champion told CNN's Open Court. "He can be No. 1 in my mind."
      Rafter -- who retired in 2002 before a brief comeback in 2014 -- admits, however, that the unpredictable Kyrgios needs to combine a disciplined lifestyle with mental toughness if he is to make good on his potential.
      "He's a real mystery to me at the moment," said Rafter, who last week took part in the Champion's Tennis tournament at London's Royal Albert Hall. "I don't know how he's coping with things mentally."
      "He's got the potential, we all know that, but is he training hard? Is he doing all the right things? Is he mentally prepared? I can't answer those questions. I don't know how he's going to go."
      While there has never been any doubt about Kyrgios' natural talent, Rafter questions whether the volatile Aussie is capable of withstanding the physical demands of the Tour.
      "I think game-wise Nick can do it. I don't know about physically; you have to be an all-round good athlete as well. Can he back up seven matches (the number of consecutive wins it takes to earn a grand slam title)?" Rafter asked.
      "Aussie Open? Probably not. French Open? Definitely not. US (Open)? No. But Wimbledon he certainly can," he declared confidently.
      Kyrgios, who finished the 2016 season as world No. 13, is still without a coach after sacking countryman Todd Larkham a week before Wimbledon 2015.
      Operating without a full-time coach is rare for a player of Kyrgios' stature, although Roger Federer also operated without a coach for a significant part of his career.

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      His lack of focus was palpable at Wimbledon in July when he faced his friend Andy Murray in the fourth round.
      The 21-year-old prepared for his Centre Court match by watching compatriot Lleyton Hewitt play doubles -- a move that was harshly criticized by commentators, including John McEnroe.
      Kyrgios committed a slew of unforced errors -- some a result of unnecessary trick shots -- and didn't even bother to sit down during a crucial changeover. Eventual Wimbledon champion Murray won easily to go up 5-0 in their head-to-head record.
      "I think when things get tough, I'm just a little bit soft," Kyrgios admitted after the match -- before getting to the heart of what has been troubling his career. "I don't love the sport. But, you know, I don't really know what else to do without it."
      Instead, Kyrgios has spoken of his love of basketball, and his wish to retire from tennis at the age 27 to pursue hoops professionally in Europe.
      That leaves just six years for him to fulfill his tennis potential. Can he do it?