The word "DOPING" is printed in capital letters inside a red circle with a slash through it on the box containing the over-the-counter spray sold in Italy that caused No. 1-ranked tennis player Jannik Sinner to fail two drug tests in March.

Sinner was cleared last month and will play Jack Draper in the U.S. Open semifinals Friday.

Trofodermin, which contains the banned anabolic steroid Clostebol, is available without a prescription in Sinner's home country, and that's where the 23-year-old's physical trainer bought the medication that led to a trace amount of Clostebol showing up in his test results.

A small can of Trofodermin was purchased for 14.50 euros ($16) at a Rome pharmacy this week by an Associated Press reporter.

The product is meant for treating cuts and scrapes and contains an underlined warning in Italian on the medication guide that comes inside the box: "For those taking part in sports: use of the drug without therapeutic needs constitutes doping and can result in positive anti-doping tests."

Giovanni Fontana, an Italian lawyer who represents athletes facing doping charges, has worked on about 100 such cases over 30 years. Ten of his cases resulted from positive tests for Clostebol that were traced to Trofodermin; nine of those resulted in bans, Fontana said in an interview Thursday.

"When an athlete tests positive for Clostebol, the first thing I ask them is if they used Trofodermin," Fontana said. "And if they haven't, I tell them to go check if a family member or partner has, because it's transmitted so easily."

Sinner was not suspended for his positive tests after it was determined the Clostebol entered his system unintentionally through a massage from his physiotherapist, Giacomo Naldi. Sinner said his fitness trainer, Umberto Ferrara, purchased Trofodermin in Italy and gave it to Naldi for a cut on Naldi's finger. Naldi then treated Sinner while not wearing gloves.

Before the U.S. Open, Sinner said he fired Ferrara and Naldi.

"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."

Ferrara, who is also a qualified pharmacist, and Naldi had been at Sinner's side during his rise, which included his first Grand Slam title at the Australian Open in January and arrival at No. 1 in June.

According to Italian law No. 376 from 2000, all products containing substances on the World Anti-Doping Association's banned list come with the printed "DOPING" warning.

"But with Trofodermin, the mark is only on the box and not the product itself," Fontana said. "So if a family member purchases the drug and throws away the box, there's a danger that the warning isn't seen."

Fontana, who represented figure skater Carolina Kostner and cyclist Filippo Simeoni — an early Lance Armstrong accuser — said Sinner could sue Ferrara and Naldi in Italy.

"It would be a civil case in which he seeks damages for the impact on his image, for the legal costs, for the anxiousness and stress he had to deal with," Fontana said.

WADA and Nado Italia, Italy's anti-doping agency, could appeal the decision in Sinner's case. Nado Italia appealed all of the Clostebol and Trofodermin cases that Fontana worked on, the lawyer said.

Fontana also suggested that Nado Italia could open proceedings against Ferrara and Naldi -- pointing to the four-year suspension for a club doctor at an Italian soccer club in 2018 for administering Trofodermin to a player.

In the United States, Clostebol is listed as a "controlled substance," meaning the government considers it to have a potential for abuse, and it can only be sold with a doctor's prescription.

Clostebol is listed in the anabolic androgenic steroids section on page 5 of WADA's 24-page list of banned substances.

And "Clostebol" appears four times on the Trofodermin box and can bought by the AP (the product is also available as a cream).

The International Tennis Integrity Agency investigation found Sinner had a trace amount of Clostebol in his system, a point he illustrated before the U.S. Open began by using eight fingers to count out the number of zeroes before the "1" in the amount, .000000001.