Both horses are from the Clifton Eventers team, and were found to have the tranquiliser reserpine in their samples when tested under the FEI's Clean Sport programme during the event which ended on September 8.

Clifton Promise's rider, Jonathan Paget, who won bronze at London 2012 as part of the New Zealand eventing team, was provisionally suspended from all national and international competition for two months pending the outcome of B-sample results and the outcome of any FEI tribunal hearings.

The same punishment has been handed down to McNab and his horse Clifton Pinot.

McNab, who is based at Bracknell in Britain, previously coached the Queensland junior squad before moving to the UK, and has mentored Paget in the past.

Equestrian Australia said it would provide guidance to McNab as he works through the options available to him through the FEI process.

The governing body's chief executive Grant Baldock has condemned the use of any banned substances and claimed that Equestrian Australia implements and fully supports the FEI and the Australian Sports Anti-Doping Authority (ASADA) anti-doping policies and guidelines.

Jonathan Paget onboard Clifton Promise whose stablemate Clifton Pinot has also tested positive for reserpine at Burghley last month