Robert Havlin has failed to persuade the disciplinary panel of the British Horseracing Authority not to reciprocate the six-month ban given to him by France Galop for failing a drugs test.
In February, the French authority said the Newmarket-based jockey had returned a positive sample at Saint-Cloud last October.
It is a major blow to Havlin, who stood himself down and twice appealed in vain to the French authorities.
“The decision to reject the application for non-reciprocation by Rab Havlin was made by the disciplinary panel, acting independently of the BHA,” the BHA said in a statement.
Havlin’s ban runs up to October 4, but he has not actually ridden in more than six months.
The Professional Jockeys Association says it will advise jockeys not to stand down in similar circumstances.
“It is bitterly disappointing that Rab’s application has been unsuccessful and his nightmare must continue for almost two more months, the result being that he has effectively been suspended for over eight months for an offence he was given six months for and did not commit in any event,” PJA chief executive Paul Struthers said.
“No other rider in future will volunteer to stand himself down in similar circumstances.
“The PJA completely supports robust testing for riders to the point that it is entirely behind and working constructively with the BHA to enhance testing for riders in Britain.
“France Galop does not operate testing thresholds designed to safeguard from false positives and therefore the risk of false positives is ever present.
“This situation was exacerbated by the fact that France Galop refused to disclose the levels present in Rab’s sample and ignored the clear medical evidence from independent hair follicle sampling that he could not have taken cocaine.”