Embattled French tennis player Richard Gasquet, who tested positive for cocaine in March, said on Friday he had never knowingly used the banned substance.
"I have never taken any cocaine in my life, I can swear it," world number 21 Gasquet told French radio Europe 1.
"It was something small, they found 150 nanograms, I have been told it is the equivalent of one tenth of a line."
Gasquet, who was provisionally suspended by the International Tennis Federation (ITF) last month, tested positive at the Sony Ericsson Open in March.
He had pulled out of the Miami tournament without playing a match, citing a shoulder injury.
If Gasquet fails to clear his name, he could face a two-year suspension from the sport.
The 22-year-old, who started his "own investigation", hinted he could have taken the recreational drug without knowing it during a party before the Sony Ericsson Open.
"I have been trying to know what happened. I can't sleep at night because of this," he said.
"I saw a person who was at that party and this person told me he/she was offered cocaine that night, that there was a lot of cocaine."
It was not clear whether the person Gasquet referred to was male or female.
"I did not see it. Had I seen it, I would have left that night club."
