Otmar Issing, the European Central Bank's chief economist, was quoted on Wednesday as saying he did not expect the current slide in the euro against the dollar to last.
Mr Issing wrote in a column in Belgian weekly Knack the retreat in the euro had less to do with the French and Dutch rejection of the EU constitution at recent referendums than with the strength of the US economy.
"A lasting slipping of the euro versus the dollar is therefore not part of the expectations," Mr Issing said.
Mr Issing also said any member state of the euro zone considering leaving the single currency should bear in mind it would have to pay "a heavy economic price".
He referred to Italian ministers' threats to leave the euro zone.
Italian Prime Minister Silvio Berlusconi on Tuesday slapped down the plan by the Northern League, a junior partner in the government coalition. In his first comments on the issue, Mr Berlusconi said it would be impossible for Italy to leave the euro and not in its interests to do so.
Mr Issing said reintroducing the lira in Italy would sink that currency, euro-denominated debts would simply "explode" and long-term interest rates would rise drastically.
"That is why I cannot imagine any government in Rome seriously considering leaving the currency union," he said.
Mr Issing also described the proposal as "irresponsible" as it increases the public's fears and further decreases confidence in the euro. Both the ECB and politicians have the duty to restore confidence in the single European currency, Mr Issing said.
"The Bank - in my view - has accurately executed its task and will continue to do so," Mr Issing added.
He said blaming the euro for the low economic growth in Europe was "misleading and unjustified".