Show jumper Ludger Beerbaum's appeal against the doping disqualification that cost the German team gold at the Athens Olympics has been rejected.
The Court of Arbitration for Sport upheld a decision that found Beerbaum and his horse, Goldfever 3, guilty of a doping offence.
The CAS said Beerbaum had made "a mistake by administering a medication containing a prohibited substance".
The horse tested positive for a banned substance, betamethasone, in Athens.
Beerbaum denied cheating, saying the substance was in cream used to treat a skin irritation on the horse.
The FEI accepted that the substance was connected to a legitimate medical treatment and agreed that Beerbaum had not tried to enhance the horse's performance or gain any unfair advantage.
But it said the rider failed to ensure Goldfever was free of prohibited substances during the event.
The CAS statement added: "He had thus committed a doping offence in accordance with the FEI [International Equestrian Federation] regulations.
"The presence of a banned substance in the urine of an athlete will automatically lead to his/her disqualification from the event in question, whether the ingestion of that substance was intentional or negligent and irrespective of the effect of that substance on the performance."
Beerbaum's disqualification saw Germany stripped of the medal, giving the gold to the United States.
Sweden moved up to silver, and Germany dropped to bronze after the FEI erased Goldfever's results.