Greece sent markets tumbling overnight and this morning after announcing plans to hold a referendum on the European debt deal designed to save the country.
The 50% haircut on Greek debt agreed at the EU summit last week has called into question the future of credit default swaps (CDS)as a hedging tool for bondholders.
Confusion over the extent of measures due to be announced at the EU summit today have sparked fresh concerns over policymakers' ability to resolve the sovereign debt crisis.
Leading banks are at odds with European policymakers after lenders offered to take a haircut of 40% on their Greek bonds, but leaders said the proposals do not go far enough.
Europe is at the centre of growing unease regarding the state of the global economy.
Greece is set to receive a further €8bn of bailout cash from the troika - the EU, IMF, and ECB - in early November, buying it more time to avoid a hard default.