The case of Nick Kyrgios and his form is a curious one in the world of tennis.Despite many touting the Australian to become one of the sport's greats, he has failed to transfer the hype into competitive trophies.Kyrgios was knocked out in the semi-finals of the Queen's Club Championships last month at the hands of Marin Cilic.However, the 23-year-old suffered a defeat against Kei Nishikori last weekend at Wimbledon in the Round of 32.The Australian has failed to reach further than the quarter-finals at Wimbledon so far in his career.He did so in 2014 at the ripe old age of 19, a tournament in which he pulled off a stunning win over Rafael Nadal.Tennis Hall of Famer and former Wimbledon champion John McEnroe believes Kyrgios' frustrations are due to mental barriers.On Radio 5 Live's 6-love-6 show, he said: "His problem is fear of failure. That's his problem, he's afraid to compete, to lay it on the line and give it his best."There are a lot of people who have that problem, that's why I admire Rafael Nadal so much. The guy goes out and plays every single point like it's the last he's ever going to play."

However, McEnroe insists that Kygios' youthful naivety could also be the cause for his disappointing form.

He continued: "He (Kyrgios) is a great kid, he's a good team player. But he seems so afraid and his opponents actually are happy about it because otherwise, the guy would be number one in the world right now."

Tim Henman then responded, joking about how those in the referees' box should fine him before a game so he would relax and concentrate.

McEnroe replied: "I wish that we could get him to go and be the type of player he could be. We are all hoping and praying for that in the tour."