The final Grand Slam tournament of the year begins Monday on the heels of a revelation that has roiled the tennis world: The world’s top-ranked player, Jannik Sinner, had twice tested positive for a banned substance earlier this year but was allowed to continue competing.

Now, less than a week after Sinner’s case was made public, the 23-year-old Italian will compete as the top seed in the men’s singles event at the U.S. Open in New York.

On Friday, Sinner spoke publicly for the first time since the story broke, telling reporters he felt “relieved” at the decision by the International Tennis Integrity Agency to clear him of fault, even as the timing of the announcement days before a major event had caused a storm of media attention and criticism from competitors.

“It’s not ideal before a Grand Slam. But in my mind, I know that I haven’t done anything wrong,” Sinner said. “I always respect these rules, and I always will respect these rules of anti-doping.”

What happened with Jannik Sinner’s failed tests?

The controversy centers on a pair of urine tests that Sinner failed over an eight-day period in March, testing positive both times for “low levels” of a banned substance called clostebol, according to the ITIA.

Clostebol is an anabolic steroid that has a history of use as a performance-enhancing drug in sports. (In 2022, San Diego Padres star Fernando Tatis, Jr., was suspended for 80 MLB games after testing positive for the drug.) In the U.S., it is designated a Schedule III controlled substance.

The drug is also used in topical skin treatments. In Italy, where Sinner and his fitness team are from, treatments containing clostebol are readily available over the counter.

In his appeal to the ITIA, which oversees doping in tennis, Sinner said that he was unknowingly exposed to the drug through two members of his staff at the BNP Paribas Open tournament in California in March.

According to arbitration records released by the ITIA, Sinner’s physiotherapist accidentally cut his finger and treated the wound each day with a medical spray called Trofodermin, which contains clostebol, that had been purchased in Italy and brought to California by a second member of Sinner’s entourage, a fitness coach.

Then, without washing his hands or wearing gloves, the physiotherapist massaged Sinner’s body and helped him with foot exercises, the records state.

Ultimately, Sinner was cleared of fault, although the arbitrator vacated his results at Indian Wells, forcing him to return $325,000 in prize money.

Is this kind of explanation plausible?

In Sinner’s case, a panel of three independent experts convened by arbitrators, two of whom were unaware of the player’s identity, found the explanation plausible.

Italy’s Jannik Sinner speaks to the media during a press conference ahead of the 2024 U.S. Open. The world’s top-ranked player has twice tested positive for a banned substance earlier this year but was allowed to continue competing.

Jamie Squire/Getty Images

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Jamie Squire/Getty Images

One, David Cowan, who once led a World Anti-Doping Agency-accredited laboratory at King’s College London, added “the minute amounts likely to have been administered would not have had […] any relevant doping, or performance enhancing, effect.”

Clostebol has been linked repeatedly to Italian athletes, in part because of its widespread availability in Italy without a prescription.

“As an Italian athlete with Italian medical staff, you would think they would be aware of this issue and be a little more mindful to avoid that kind of contamination,” said John Gleaves, a kinesiologist at California State University, Fullerton, who tracks doping cases.

On Friday, Sinner said he had fired the two members of his team involved — both the physical therapist who used the drug, and the fitness coach who had purchased it and traveled with it to California.

“Because of these mistakes, I’m not feeling that confident enough to continue with them,” Sinner said. “The only thing I need right now is some clean air. I was struggling a lot in the last months.”

Athletes have often been absolved of fault in doping cases by arguing that they had been unknowingly exposed to the banned substance, Gleaves said. The ingestion of contaminated meat is one common explanation, or other environmental exposure, as seen in the case of the Chinese swimmers whose positive tests for a banned substance were publicized earlier this year before the Paris Summer Olympics.

“We’re seeing a lot more of these cases that really point to an athlete not having intended to take something in and having it getting into their body in a level that’s below a threshold that would be performance-enhancing — but is at a threshold where it can be detected,” Gleaves said.

What have Sinner’s competitors said?

Sinner was allowed to continue to compete while arbitrators considered his case. Between the tests in March and their revelation last week, he competed in eight tournaments, including the French Open and Wimbledon. (Notably, he withdrew from the Olympics over a case of tonsillitis.)

That came in contrast to some other cases of doping in tennis. Two-time Grand Slam winner Simona Halep was provisionally suspended for more than a year while arbitrators considered her case and ultimately found that she had acted with “no significant fault.”

The revelations about Sinner inspired strong reactions in the tennis world last week.

“Different rules for different players,” wrote Denis Shapovalov, a Canadian player scheduled to play Monday in the U.S. Open’s first round.

“Ridiculous – whether it was accidental or planned. You get tested twice with a banned (steroid) substance… you should be gone for 2 years,” wrote Nick Kyrgios, the Australian who was the 2022 runner-up at Wimbledon.

On Friday, Sinner said he had been allowed to continue playing because of the speed with which he was able to identify the source of the banned substance and provide evidence to international authorities.

Still, he acknowledged his competitors’ frustration.

“Obviously it has been a very tough moment for me and my team. It still is. It’s quite fresh, everything,” he said. “I also know who is my friend and who is not my friend now, because my friends know I would never do that.”