The Court of Arbitration for Sport (CAS) has imposed a four-year ban on American sprinter Erriyon Knighton after rejecting his defense that steroid traces in his system came from contaminated beef.

Knighton, 20, is a two-time World Championships 200 metres medallist, winning bronze in Eugene in 2022 and silver in Budapest in 2023. Considered one of track and field’s brightest young stars, he tested positive for epitrenbolone, an anabolic steroid, during an out-of-competition test on March 26, 2024.

Although provisionally suspended between April and June 2024, Knighton was initially cleared by a U.S. tribunal, which accepted his claim that the banned substance could have come from imported meat. The ruling allowed him to compete at the Paris Olympics, where he narrowly missed the podium with a fourth-place finish in the 200m final.

However, the World Anti-Doping Agency (WADA) and World Athletics appealed to CAS, arguing that his explanation lacked scientific credibility. In its decision, the court agreed, saying Knighton’s “meat contamination scenario fell short of the required proof of source and was statistically impossible.”

“There is no proof that would support the conclusion that oxtail imported into the USA would be likely to contain trenbolone residues at the level required to have caused the athlete’s Adverse Analytical Finding,” CAS stated.

The four-year suspension will be applied retroactively, covering the period from March 26, 2024, to April 12, 2024. Knighton was not included in the U.S. squad for the World Championships in Tokyo, which open this weekend.

WADA welcomed the ruling, saying in a statement: “We are pleased with the outcome and will continue to appeal cases to CAS when we feel justice has not been served.”

The decision represents a dramatic setback for Knighton, once tipped as the natural heir to Usain Bolt in the 200 metres.