Ireland are likely to lose their only gold medal of the Athens Olympics after a second blood sample taken from Waterford Crystal tested positive for banned substances.

In a statement issued by his lawyer on Tuesday, rider Cian O'Connor said he had been unofficially informed that "minute traces of the medications fluphenazine and zuclopenthixol have been found".

The Equestrian Federation of Ireland (EFI) said it had not yet been officially informed of the test results by the world governing body.

However, official confirmation of the 'B' sample will almost certainly lead to the Irish rider being stripped of the gold medal.

Waterford Crystal had been administered the human forms of the psychiatric drugs so the horse could be treated in a water therapy pool, O'Connor's vet James Sheeran added in the same statement.

"I chose these drugs because I wanted a calming effect without making him sleepy or unsteady on his feet, as equine medicines would," he said.

For each sedative a "fraction of a millionth of a gram had been found", according to O'Connor.

"These readings are so minute that they confirm what I have said throughout this matter, that they had absolutely no therapeutic or performance-enhancing effect on my horse at the Games themselves."

The rider, whose mount ABC Landliebe also tested positive for the banned sedative at an event in Rome earlier this year, said the schizophrenia drug had been given to both horses in their best interests and during rest periods.

BIZARRE TWISTS

O'Connor and his vet have denied any wrong-doing and the show jumper recently accused unnamed enemies of trying to destroy him after a series of bizarre twists, including the theft of documents in Ireland and a test sample in England.

The EFI said last month that an initial, or 'A', sample taken from Waterford Crystal at the individual show jumping competition in Athens was positive.

The horses of two high-profile German riders also failed dope tests at this year's Olympics.

The 'B' samples from Goldfever, ridden by Ludger Beerbaum in the team show jumping, and Bettina Hoy's three-day eventer Ringwood Cockatoo are also being tested.