The first feedback from a team of European Commission experts seconded to Athens produced "few concrete steps" forward, said Horst Reinchenbach, the German head of a task force trying to help Athens reform its economy.
"Solutions are being explored to provide Greece with an adequate way to increase tax revenue, taking into account the vast amounts channeled to Switzerland by Greek nationals," Reinchenbach's first quarterly report said.
"We want Greece to get the best deal possible using EU and IMF experience and legal support," added an EU official on condition of anonymity.
This official said that of the missing €60 billion ($81 billion) in tax revenues identified by the International Monetary Fund, just half is "theoretically collectible" and only €8.0 billion likely to be recovered "sooner or later."
Athens wants to try and emulate direct deals done with Switzerland by Germany and Britain in recent months to recover proceeds due from hidden assets.
Swiss media have estimated that some 350 billion francs (€282 billion) in Greek assets are hidden in Switzerland.
However, a study by Bank Helvea on hidden assets from 2009 puts undeclared Greek funds at just 24 billion francs.
The Swiss National Bank said some 4.1 billion francs in Greek assets were held in 2010 in the alpine state, which has come under international pressure over its traditional bank secrecy laws.
Reinchenbach's report said a daunting job lay ahead.
This has become all the more important since targets for revenues from Greek state privatisations were revised heavily downwards by the outgoing government as a result of the recession, from 5.0 billion euros by the end of 2011 to just €1.3 billion.
Meanwhile, a plan to build a new motorway network forecast to add two percentage points to the country's growth over coming years, is snarled up in litigation involving many of Europe's biggest civil engineering firms, Reinchenbach said.