Boris Becker took aim at his former protege Holger Rune by brutally agreeing that he is still too “immature”.

The retired German tennis star coached the world No. 13 at the end of the 2023 season and the start of 2024 before stepping down.

But it seems Becker believes the Dane has regressed as he endorsed a damning analysis of Rune’s game.

Becker returned to the coaching circuit a year ago, joining Rune’s team for the European indoor hard-court season. They enjoyed instant success - Rune reached the Basel semi-final, the Paris Masters quarter-final, and qualified for the ATP Finals for the first time.

The 56-year-old shared his intentions to continue working with Rune this season. But he announced that he was stepping down from the head coach role in February.

Since then, Rune has had a relatively disappointing season, failing to win a title and dropping out of the top 10. He started to rediscover his form at the Paris Masters, reaching the semi-final.

But he lost a one-sided match to Alexander Zverev and tennis analyst Jim Courier gave a brutal assessment of his tactics, calling him “immature”. And Becker was quick to agree.

“I, for one, have no idea what he’s trying to do here,” Courier said on Tennis Channel. “It’s all just happening instinctively - it’s like a full-blown jazz exploration out here.

“No rhyme, no rhythm. There’s a lot of great things happening, it’s just all scattershot and that is not a recipe for long-term success. It’s still a very immature game.

“If he wants to be with the big boys consistently, he’s gonna have to find something he can rely on rather than throwing paint against the wall and seeing what it looks like when it’s all said and done. He just needs a sense of order - doesn’t have it.”

Even though he was responsible for Rune’s game at one point, Becker backed up Courier’s argument. The six-time Grand Slam champion reposted the American’s words on social media and wrote: “Jim knows what he’s talking about!”

It’s not the first time Becker has turned his back on Rune since their split. He recently claimed the Dane had regressed and named Ben Shelton as the next young guy to challenge the duopoly of Carlos Alcaraz and Jannik Sinner.

“The one who for me is closest to reaching the top is Ben Shelton,” he told Gazzetta dello Sport.

“The most prepared, at the beginning, seemed to be Holger Rune, but he has not progressed much this year.

“However, I also watched the American for a long time at the Laver Cup, in singles and doubles, and I liked his attitude. He smiles, puts on a show and has fun.”