Nick Kyrgios and tennis legend Martina Navratilova have expressed their concern for Andrey Rublev after another outburst from the Russian star in a US Open loss to Grigor Dimitrov.

Dimitrov returned to the US Open quarter-finals for the first time since 2019 with a five-set triumph over Rublev on Sunday, winning 6-3, 7-6 (7/3), 1-6, 3-6, 6-3 to set up a clash with either Frances Tiafoe of the United States or Alexei Popyrin, the conqueror of Novak Djokovic, for a place in the semi-finals.

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Rublev, who made headlines in July after a stunning Wimbledon meltdown, struggled to control his emotions against Dimitrov and at one point suffered an injury after repeatedly hitting himself with his racquet.

Rublev’s hand started to bleed and while there was not much damage, it was enough to require treatment during the changeover.

“That’s when I get a bit worried,” Kyrgios said in commentary on ESPN.

“When you start hurting yourself and it hinders your performance. I much prefer when he hits his shoe, not his hand or his head.”

Navratilova, meanwhile, said on Sky Sports that Rublev “beats himself” and that his “negative energy” continues to work against him in matches.

“He just keeps making the same mistake over and over again,” Navratilova said.

“You are worried for him. Come on, just get it together. You are only hurting himself, literally physically and emotionally. He needs to save his energy for good stuff, like hitting tennis balls. Not hitting his head.

“He’s got the game to win a major, I believe that. He’s got the big serve, the big forehand and he just needs to improve his net game a little.

“The sky is the limit. The guy has got it all. He just needs to work on the mentality. He is such a lovely guy.”

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The 33-year-old Dimitrov, meanwhile, made the semi-finals in 2019 where he was defeated by Daniil Medvedev having stunned five-time champion Roger Federer in the quarter-finals.

“I was playing fairly good,” said Dimitrov, the oldest player left in the men’s draw.

“But for some reason my body got tired a little bit and he wasn’t going to give up the match. I had stay patient. I think the biggest thing today was my experience.”

Dimitrov saved 13 of 18 break points in the match and credited long-time friend and six-time women’s champion Serena Williams for a helping hand.

“She gave me a good pep talk yesterday,” he said of the US tennis legend who was watching the match in Arthur Ashe Stadium.