Former US Open champion John McEnroe has hailed Australian star Nick Kyrgios as playing the best tennis he’s ever played, but did warn that is “not impossible” that he could walk away from the sport after the US Open. Kyrgios, 27, produced one of the performances of his career as he beat number one seed Daniil Medvedev in four sets on Sunday evening, in what was one of the games of the tournament. Ad Speaking afterwards Kyrgios made vague comments about this being the end of his journey in tennis, which led to intense speculation about his future.