The B sample from Clifton Pinot, taken from the horse after its 14th placing at the Burghley Horse Trials in September, has tested positive for the long-acting sedative, reserpine.
Clifton Pinot was ridden by Australia’s Kevin McNab.
Clifton Promise, another horse from the Clifton Eventers stable, which New Zealander Jonathan “Jock” Paget rode to victory at Burghley, has also returned two positive samples for reserpine, more commonly known as Rakelin.
Equestrian Australia confirmed yesterday it had received notification from the International Equestrian Federation confirming the B sample result from Clifton Pinot.
In accordance with FEI processes, McNab must now provide a written explanation to the FEI.
Equestrian Australia said it had spoken to McNab, who was considering his options.
McNab has been provisionally suspended from international and national competitions since the positive A sample finding.
Equestrian Australia chief executive Grant Baldock said that as the case was ongoing, he could not make any further comment at this time.