Mohammad Samim Faizad, one of only six Afghans at the Paris Olympics, denied intentionally doping on Saturday after he was provisionally suspended having failed a test for a banned steroid.
The 21-year-old judoka, who was beaten 11-0 in the French capital on Tuesday in the men's -81kg category, had told AFP on the eve of the Games that competing at the Olympics was a dream come true.
He was provisionally suspended on Friday after a test "returned an adverse analytical finding for the non-specified substance stanozolol metabolites", the International Testing Agency said.
Faizad spoke out in a video shared by Afghan media on Saturday.
He said he was injured four months ago while at a training camp in Uzbekistan and was under treatment, suggesting that was why his test was positive.
"I'm an athlete, I'm not a medical expert. How should I know if a medicine has steroids in it or would produce a positive doping test?" he said.
The sample from Faizad was collected by the ITA on the day he lost to Austria's Wachid Borchashvili in his opening bout.
There are three men and three women representing Afghanistan at the Games.
Of the six, Olympic debutant Faizad was the only one who trained for the Games inside his Taliban-controlled homeland.