Outgoing World Bank chief Robert Zoellick says European leaders dealing with the sovereign debt crisis have done too little too late and warns that Europe risks losing influence.
In interviews with European publications, Mr Zoellick urged Europe to act quickly.
He told Germany's Der Spiegel magazine that European politicians "always act a day late and promise one euro too little. Then, when it gets tight, they add new liquidity."
This bought time but did little to address the euro zone's structural problems, he said.
Mr Zoellick said Germany should take a leadership role and keep pushing for fiscal and structural reforms.
He said while a Greek exit from the euro would have enormous consequences, Europe should not allow itself to be held hostage by Athens.
"If the Greek leadership threatens to leave the euro zone, then the rest of Europe must have developed a mechanism to cushion that," he said.
In a separate interview with Britain's Observer newspaper, Mr Zoellick warned of the risk of a "Lehmans moment" if the crisis is not properly handled - a reference to the bankruptcy of US bank Lehman Brothers in September 2008 that triggered a global financial slump.
Zoellick steps down as World Bank president on 1 July and will be succeeded by Korean-born US health expert Jim Yong Kim, who was nominated by US President Barack Obama for the post.
The euro zone will be on the agenda at a G20 summit from Monday in Mexico, overshadowed by mounting fears about Spain and Italy.