Greece are to appeal to the Court of Arbitration for Sport (Cas) after weightlifter Leonidas Sampanis was stripped of his bronze medal.
Sampanis was third in the 62kg category but a doping test showed up twice the allowed amount of testosterone.
But prosecutor Grigoris Peponis, who has opened his enquiry into claims, Sampanis could have been slipped a banned substance without his knowlege.
Sampanis is the first weighlifter to be stripped of his medal in Athens.
A total of seven lifters have failed doping tests in the build-up to the Games while another two tested postive in Athens.
Doctors established the testosterone came from outside the body but Sampanis, who had won silver at the previous two Olympics, is maintaining his innocence.
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This is a sportsman that over the years has never committed a doping offence and is an outspoken advocate against doping
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Greek Olympic chief
Giannis Papadoyiannakis
"I want to thank all the people who are with me and have given me courage," Sampanis said.
"The case has been taken over by my lawyer, a prosecutor and the federation and I hope that all together we will be vindicated.
"I am telling you I am innocent."
Sampanis was also being backed by Greek Olympic chief Giannis Papadoyiannakis.
"We will be taking every legal measure possible, every legitimate procedure will be followed so as to shed ample light into this case," said Papadoyiannakis.
"This is a sportsman that over the years has never committed a doping offence and is an outspoken advocate against doping."
Greece's two biggest track medal hopes, Kostas Kenteris and Katerina Thanou, were withdrawn from the Games after they missed a drugs test in mysterious circumstances just before the Games began.
The Greek government vowed on Friday to crack down on any athlete who tests positive for banned substances.