John McEnroe blasted Nick Kyrgios as a "bonehead" after the Australian's latest antics in his first-round U.S. Open loss to Andy Murray.
Kyrgios, 20, appeared to try to take a nap during one of the changeovers, smashed his racket and launched an expletive-laden rant at umpire Carlos Ramos for allowing fans to enter the stadium during one of his service games.
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But it was Kyrgios' failed attempt at a between-the-legs half-volley as he pressed to try to break Murray's serve in the second set that drew the ire of four-time U.S. Open champion McEnroe.
McEnroe said of the shot on ESPN: "An absolute brain freeze. Absolute stupidity. He could have volleyed that away for another break-point chance.
"I hope he learns from these bonehead moves. He should be a seed already, at least 20. You don't want to be remembered as a clown. You want to be remembered as a player.
"So he better step up. Otherwise he won't be talked about too much. He thinks he's a vaudeville entertainer. I don't know what's going on here."
Murray, the world No. 3, proved too strong for Kyrgios as the two-time Grand Slam champion and winner at Flushing Meadows in 2012 won 7-5, 6-3, 4-6, 6-1.
Kyrgios has courted controversy in 2015 and was fined by the ATP last month after a Rogers Cup match with Stan Wawrinka in which he told Wawrinka that fellow Australian Thanasi Kokkinakis had slept with Wawrinka's girlfriend.
Kyrgios recently turned to former world No. 1 Lleyton Hewitt to mentor him, but Tuesday's performance from Kyrgios was overshadowed by on-court histrionics at Arthur Ashe Stadium.