A Greek withdrawal from the euro would cause "unpredictable, irrevocable damage" to the single currency that "no rational person" should advocate, Nick Clegg will warn today.
In a speech in Berlin, the Deputy Prime Minister will criticise the notion "being whispered behind cupped hands" that Greece's exit could be a good thing for the rest of Europe.
He will say that Europe must show leadership to find a way out of the crisis and address the problems arising from the lack of fiscal coherence in the eurozone.
"We have got to hit back against this fatalism which says that Europe can't fix this," he will say.
"And by the way, let me challenge the fashionable assumption being whispered behind cupped hands - that for some countries, leaving the euro wouldn't be that bad, that actually a Greek exit now would be in everyone's best interests.
"My own view is that that wildly underestimates the unpredictable, irrevocable damage that could be done to a monetary union when it is shown not to be permanent.
"No rational person interested in the wealth and wellbeing of Europe's citizens could advocate taking such a risk: not with Greece's future, or our own."
Mr Clegg, travelling to Berlin with Business Secretary Vince Cable, will visit a Siemens turbine factory and launch a Queen Elizabeth prize for engineering.
He will say in his speech that the response to the eurozone crisis has been "woefully fragmented" and that the decision-making process, lurching from one crisis summit to the next, is undermining public confidence.
"The tree is falling, and we are pruning one leaf at a time. It is piecemeal politics - endless tactics with no strategy," he will say.
"So we must gather these overlapping problems together and solve them as one. This is a European crisis. It must be solved at the European level."
Mr Clegg will say that one of the euro's problems is the "common monetary policy without shared fiscal arrangements".
Europe must either "share common debt, or change the way money is transferred", he will say.
"You cannot have a monetary union in which one country saves, exports and invests and another spends, borrows and consumes without some mechanism to make it all add up," he will say.
"So we need new fiscal instruments in the eurozone, through either eurobonds or greater transfers between eurozone members."
Mr Clegg will warn people in Britain that the crisis in the eurozone is not a "distant irrelevance".
"3.5 million British jobs depend on the EU economy, and 40% of our exports go to the eurozone. Culturally, economically, and socially, we share in so much more than we differ. So Europe's future is our future. We must do everything we can to secure it," he will say.
His comments will come after David Cameron called for a "lasting solution" to the eurozone crisis after enduring 18 EU summits on the subject since he became prime minister.