When Jannik Sinner tested positive for the banned substance clostebol in March 2024, it sent shockwaves through the tennis world. The Italian star was eventually cleared by the International Tennis Integrity Agency (ITIA), but the World Anti-Doping Agency (WADA) pushed for a ban that sidelined him for nearly three months. Now, almost two years later, clostebol has returned to the headlines, ensnaring two lower-ranked players in a fresh doping controversy.

The ITIA has provisionally suspended Latvia's Karlis Ozolins (currently ranked No. 744) and American Daniil Kakhniuk (ranked No. 1,112) after both tested positive for clostebol. The players provided samples during an ITF World Tennis Tour event in San Jose, Costa Rica, on February 17. Subsequent tests revealed metabolites of the banned steroid, triggering automatic provisional suspensions under tennis's anti-doping rules.

Clostebol is a synthetic anabolic-androgenic steroid derived from testosterone. While it has legitimate medical uses—such as topical treatments for skin conditions and eye preparations—its performance-enhancing effects have made it a target for anti-doping authorities. The substance also appears on WADA's annual prohibited list, alongside other anabolic agents, due to its ability to boost muscle growth and recovery.

The drug's notoriety in sports dates back decades. It has been used illegally in both human and animal contexts, including in cattle to promote growth. This latest case adds another chapter to tennis's ongoing struggle with clostebol, which first gained widespread attention during Sinner's high-profile ordeal. For Ozolins and Kakhniuk, both grinding on the lower tiers of professional tennis, the road back could be long—even if they ultimately prove their innocence.