World 100m champion Torri Edwards is out of Athens, after her appeal against a two-year drug ban was rejected.
Edwards claimed she took drug by accident
The Court of Arbitration for Sport (CAS) chose to uphold the punishment imposed by the US Anti-Doping Agency.
The 27-year-old sprinter received the ban after testing positive for the stimulant nikethamide at an athletics meeting in Martinique on 24 April
Edwards, who was scheduled to run in the 100m and 200m in Athens, claimed she took the substance by accident.
The CAS announced its decision after meeting for six hours in Athens on Tuesday.
In its report, the organisation found there was "negligence on the part of Ms Edwards and also negligence on the part of support personnel employed by her".
It added: "In those circumstances a two-year sanction which is the uniform standard sanction imposed by the WADA Code does not violate principles of
fairness in sport - even though it may appear to be harsh."
Devers will be going for her third 100m gold
Edwards maintained she had ingested the banned substance through a glucose tablet, which she had taken after feeling unwell before a meeting in Martinique.
Her defence team had prepared a seven-point argument against the ban, but the CAS decision means Edwards has no further right of appeal.
Her place in the 100m will go to 37-year-old veteran Gail Devers - twice Olympic champion over that distance. Lashaunte'a Moore will step up in the 200m.
Ironically, Edwards was crowned world champion when compatriot Kelli White was banned after admitting taking drugs.