Nick Clegg has warned eurosceptic Conservatives pushing for an in-out referendum against "putting the cart before the horse".
The deputy prime minister used a newspaper interview to speak out against the increasing pressure faced by David Cameron from the Tory leader's backbenchers.
"For the life of me I still don't know what is the question we're supposed to be putting to the British people because we don't yet know what we're reacting to in terms of the further integration of the eurozone," Clegg told the Guardian.
"It's an exercise of political shadow boxing to try and anticipate a process of which we're not one of the principal authors and then start now prescribing how we should react to it."
The Fresh Start group of Conservative MPs is set to call for a renegotiation of Britain's powers and the EU's competencies in a pamphlet due out in the new year, however.
Clegg added: "What we really should be doing is just focusing on the kind of economic firestorm at hand, working co-operatively to help them to put out the fire in the eurozone and to come out of this phase of economic emergency.
"I think to have a referendum, kind of about nothing very much in particular, when you're in the middle of an emergency repair job to your own economy and European economy, is putting the cart before the horse."
Cameron has already conceded a referendum could take place in the next parliament. Some eurosceptics want the government to legislate to guarantee such a vote will take place, but the prime minister has dismissed as unnecessarily binding.
Clegg's Liberal Democrats are inherently pro-European and have made clear they will resist any attempt to bring forward a referendum in the short-term. That has not stopped Conservative speculation about the possibility of Britain's withdrawal from a two-tier Europe, in which Britain is pushed to the fringes of an increasingly politically integrated eurozone.
"It would be a dramatic reversal of not just decades but centuries of British engagement and leadership if we were to suddenly back ourselves out of the whole enterprise, but it would also in my view have a very detrimental effect on the balance of opinion, the balance of debate in the rest of Europe," Clegg insisted.
Work and pensions secretary Iain Duncan Smith is among those who have publicly suggested Britain could prosper from outside the EU - a view fundamentally at odds with that of the deputy prime minister.
"It short changes us as a country to assume always that we cannot lead when all the evidence is, throughout our history, even if we're not in the centre of the action that's going on across the Channel, that we nonetheless can bring great leadership to bear," Clegg said.