"What do they need, another 15 billion euros? If you think that is the last 15 billion that they will have miscalculated, then best wishes," Klaus-Peter Mueller told an industry event in Frankfurt.

"They will come back for more and there will be no end, unless you really see them enact structural reforms, but this won't take just two-three years -- we're talking 20, 30 or 40 years for Greece."

Mueller said it doesn't do any good to Greece were euro zone governments to continue forcing them to wear the "shackles" of a currency that only permits internal adjustments via spending cuts and declining wages.

"The Greeks need on balance a currency that they can then devalue," Mueller said, adding it would take a long time before the government could build up from scratch functioning structures that restore competitiveness.

Athens and its EU partners have long ruled out a euro exit, which could drag the bloc even deeper into crisis. However, earlier in January a Greek government spokesman said the country would have to leave the euro zone if it fails to clinch a deal on a second, 130 billion euro bailout with its international lenders.

The chairman of Germany's second largest listed lender disagreed that an exit would prompt "global chaos" and cause investors to dump sovereign debt from other periphery countries like Italy and Spain.

"I don't think that markets would react negatively towards the other countries that would then remain in the euro zone after such a decision," he said.

(Reporting by Christiaan Hetzner)