Ash Barty's coach has sensationally drawn a line through his superstar charge's chances of completing a coveted career grand slam unless US Open officials change the balls.
Barty's watershed Australian Open triumph on Saturday earned the world No.1 her third career major following French Open glory in 2019 and magical Wimbledon ride last year.
After defeating American Danielle Collins 6-3 7-6 (7-2) in a thrilling Melbourne Park decider, the US Open is now the only remaining slam to elude Barty.
But despite joining the legendary Serena Williams as the only active women's player to have won majors on clay, grass and hard courts with her home slam breakthrough, Barty can't contend for the title in New York under the current playing conditions.
That's the verdict of her trusted mentor Craig Tyzzer, anyway.
Barty suffered a shock third-round loss to world No.43 Shelby Rogers at Flushing Meadows in September in what has turned out to be the Queenslander's only defeat in her past 19 hardcourt outings.
The world No.1 also won prestigious events on the surface in Miami and Cincinnati last year and Tyzzer says her early exit from Flushing Meadows was no coincidence.
"The US Open really needs to change the ball for the girls. The fact they still use a different ball for guys and girls, it's a terrible ball for someone like Ash," Tyzzer said on Saturday night.
"Even in Cincinnati, when they use the US Open ball outside, she could actually get some loft out of the court.
"But the ball itself is so light. It was the only tournament last year and really for two years where she uses gut racquet (strings) but I had to change her to a poly just to get any sort of control of the ball.
"If they keep that ball the same, no one like Ash will win that tournament."
With no disrespect to the two shock finalists, British qualifier Emma Radacanu and unseeded Canadian Leylah Fernandez, Tyzzer said he wasn't the least bit surprised to see an all-unseeded final in New York last September.
"You see the result at the US Open, it was two players who, you go, 'wow, that was, two different players won that?' There's no surprise when the ball is like it is," he said.
"And I don't know the reason why it's the only tournament that has separate ball for the guys and girls.
"So if they don't change the balls, she (Barty) won't win the US Open."
Despite his stunning assertion, Tyzzer believes hard courts are Barty's best surface and says even he's "in awe" of what the 25-year-old has accomplished.
"I mean, she loves grass, but Wimbledon is so different in that it's really slow, like it's a slow surface, it's a different grass," he said.
"So a lot of players find that quite difficult where Ash quite enjoys the really low bounce and the slowness there.
"But I always thought her first win, in a grand slam, would be on a hard court.
"But typical for her she proved me wrong and she won on clay first and then grass and then now hard court.
"Yeah, look, it's amazing that she's been able to do it. It's pretty impressive.
"We've all got to sit back and just look at what she's been able to do on different surfaces and just her ability to play the level of tennis that she does.
"Sometimes I'm just in awe of it."
