United States sprinter Erriyon Knighton has been handed a four-year ban after the Court of Arbitration for Sport partially upheld appeals from World Athletics and the World Anti-Doping Agency against a decision not to suspend him.

The 21-year-old tested positive for trenbolone - a banned substance used for muscle growth - in March 2024.

He avoided a ban following an independent arbitrator's ruling and was cleared to compete at the 2024 Olympics, but is now banned with immediate effect.

Knighton, who finished fourth in the 200m in Paris last summer, was not selected in the USA team for the World Championships, which take place from 13-21 September in Tokyo, Japan.

He was intially cleared after submitting evidence claiming the adverse findings were due to meat contamination.

World Athletics and Wada found the evidence "fell short of the required proof of source" and was "statistically impossible", and Cas has now ruled in their favour.

"The Cas panel determined that 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 said.

Meanwhile, Ethiopian middle distance runner Diribe Welteji will also miss the World Championships after Cas upheld a provisional suspension while her doping case is heard.

The 23-year-old, who won 1500m silver at the 2023 World Championships in Budapest, was charged with failing or refusing to submit a doping sample by the Ethiopian Anti-Doping Authority in late August.