The samples, provided by the veterinary clinic from the nearby town of Orahovica on 19 October, will be sent to the EU avian influenza reference laboratory at Weybridge, Great Britain, for testing.
Until confirmation comes from the Weybridge laboratory, measures will be in force in Croatia as if the disease has been confirmed.
The government has imposed a ban on the sale of poultry. The ban, however, does not apply to intensively bred poultry being sent to certified facilities for slaughter in special conditions under veterinary supervision.
All poultry must be held in closed buildings, and wild fowl hunting has been banned.
The Ministry said that all the necessary steps had been taken in the affected area to prevent the disease from spreading.