Jannik Sinner is cruising through yet another Australian Open. The Italian has powered his way into the quarterfinals, taking down compatriot Luciano Darderi in the fourth round with a stellar straight-set win, 6-1, 6-3, 7-6(2). But early in the match, Sinner ran into a minor issue with the umpire, one that reminded fans of the same problem Carlos Alcaraz faced in his R4 clash.

During the match, the No. 2 seed was among several players spotted wearing a screenless fitness tracker on court. Moments before stepping on to face Luciano, he was asked to take it off. Later, in his press conference, Sinner explained the situation openly.

“Yeah, there is a certain data we would like to track a little bit on court,” Jannik Sinner said in his press conference, “It’s not for the live thing, but it’s more about what you can see after the match, and these are the data we would also like to use in practice sessions because from that you can practice with the heart rate and how many calories you burn and all these kinds of things.”

As Sinner added, “I mean, the umpire asked me straight away if this is the tracker; I said yes. He said, “Remove it.” It’s fine; there are other things we could use. It’s the vest, but for me it’s a bit uncomfortable because you feel like you have something on the shoulders, and it’s a bit different. But rules are rules, and I understand and won’t use it again.”

The device in question was a WHOOP wristband. It’s a sleek, screenless fitness tracker that monitors biometric data like heart rate, recovery, and physical strain. It also tracks sleep, stress, and overall fitness, giving players deep insights into their conditioning beyond match play.

Earlier in the tournament, Carlos Alcaraz had faced the same issue. He too was asked to remove his WHOOP band during his match against Tommy Paul. According to International Tennis Federation guidelines, WHOOP 3.0, 4.0, 5.0, and MG models are classified as approved player analysis technology, but not for Grand Slam use.

The Spaniard also addressed the situation in his press conference, owning up to the slip:

“These are the tournament’s rules, the ATP’s, the ITF’s… You can’t play with it. It’s something that helps you take better care of yourself, to monitor your recovery, your training load… but well, I haven’t been able to use it in matches, it’s fine. You take it off and keep going,” said Alcaraz during his press conference after defeating Paul.

The ATP, which runs the men’s tour but not the Grand Slams, gave players the green light to use the technology during matches in 2024. Over on the women’s side, the WTA already embraced it, encouraging its pros to bring a data-driven edge to competition.

For Sinner, that data may have been especially useful under the fierce Australian sun. The Italian had cramped up in his previous match on Saturday against Eliot Spizzirri. To clear the air, his coach later spoke up about what went wrong.

Jannik Sinner’s coach explains what happened during his R3 match

The Australian sun showed no mercy on Saturday, with temperatures soaring to 40 degrees. The World No. 2 felt the full force of it in his third-round clash, pushing through cramps and fatigue as the Melbourne heat sapped his energy. Even then, he refused to give in, cutting rallies short and conserving just enough fuel to stay in the fight.

The brutal heat tested players to their limits, but for Jannik Sinner, it became a survival mission. He looked close to breaking at times, yet, as his coach Darren Cahill later explained, there was method behind the struggle.

“It’s clear that Jannik was very lucky with the timing of the roof closure,” Cahill said on Monday. “Everyone on the team knew that, at some point, the match would be paused to deploy the retractable roof. Our goal was for him to hold on as best as he could until the end of the third set.”

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Sinner admitted he caught a lucky break when the roof finally closed, giving him the breather he desperately needed. Even revealing his thoughts later to the press:

“I believe that I’m someone who tries to put tennis in the highest priority. And I know that I’m doing that for years now. In the back of my mind, I know how much I work. I feel well prepared, even if some problems could happen potentially on the court.”

Now, the 22-year-old is charging into the quarterfinals, where he’ll face Ben Shelton once again. Last year, he took down the American in straight sets in the semifinals before lifting the trophy for the second time. The question now: Can he make it happen again? Drop your thoughts below!