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 when riding at Saint-Cloud last October and that it would ''request the reciprocation'' of the imposed sanction by its counterpart in Britain.
It is a major blow to Havlin, who strenuously refuted the findings and twice appealed in vain to the French authorities. He said at the time he was "deeply upset and shocked'' by the suspension and that he fully expected to clear his name following what he described as an ''outrageous miscarriage of justice and defamation of my character".
In a statement, the British Horseracing Authority said: "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 did not offer a position regarding the application. The BHA's role in the hearing was to facilitate the application and to lay out to the panel the relevant Rules and the facts of the matter as we understand them.
"The application itself was submitted and presented by Rab Havlin and his representatives.
"We cannot comment on the finding itself until we are in receipt of full written reasons."
Havlin's ban runs up to October 4, but he has not actually ridden in well over six months.
The rider tweeted: "Didn't get the result we had hoped for today, another six weeks to go, thanks for all the support, #8months11days."
Paul Struthers, chief executive of the Professional Jockeys Association, expressed his disappointment at the verdict.
He said: "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.
"Rab voluntarily stood himself down in Britain whilst he attempted to clear his name in France and is now paying the price for that in circumstances where it was highly likely, if not certain, that the BHA would have acted to stand him down had he not volunteered to do so.
"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.
"However, Rab's case highlights serious concerns for all other riders heading to France. 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.
"Their testing procedures on track also leave much to be desired and the PJA will be urging the IFHA (International Federation of Horseracing Authorities) to consider these issues as part of their ongoing international harmonisation project to ensure other riders do not have to go through this ordeal."