The Equestrian Federation of Ireland has confirmed that the horse ridden in Athens by Olympic gold medallist, Cian O'Connor, has tested positive for 'prohibited substances'.
Mr O'Connor has requested that the 'B' sample taken from his horse after the showjumping competition also be tested.
There is some doubt now as to whether the medal will remain in the 24-year-old's possession.
Yesterday, the Equestrian Federation of Ireland received notification from its international governing body that Waterford Crystal had failed a doping test.
Mr O'Connor says he is utterly devastated at the news and insists that he won the medal fair and square. He says that it is his absolute belief that no performance-enhancing drugs were given to Waterford Crystal.
In the statement, he refers to an injury sustained by the horse just before the Olympics. During the course of the treatment, veterinary surgeon James Sheeran administered a mild sedative which he said would disperse from its system within two weeks.
Mr Sheeran told the EFI that if any residue of the sedative was in the horse's system it would have no therapeutic influence on the animal.
The federation says that it does not condone the use of prohibited drugs but that it stands behind the showjumper's efforts to clarify the situation.
Meanwhile, it is also reported that the horses of German riders Ludger Beerbaum and Bettina Hoy also failed drugs tests during the Athens Games.