John Capel was left out of the USA's 4x100m relay team in the semi-finals after testing positive for marijuana, the team's head coach has revealed.
Capel tested positive for the drug at a meeting on 9 August, and coach George Williams only heard about it 90 minutes before the race on Friday.
"I did not want to risk anything for him or the other three on the relay," said Williams.
A positive test for the drug, however, only carries a public warning.
As a result, Capel would have been eligible to run and will not face any ban.