France, the Netherlands, Austria, Finland and Hungary could leave.
Front National leader Marine Le Pen has pledged to hold a French referendum if she emerges victorious in next year’s presidential elections.
While for the past two months a Nexit has been on the cards after Dutch voters overwhelmingly rejected a Ukraine-European Union treaty
Details of Berlin’s concerns were outlined in a finance ministry strategy document.
Angela Merkel’s country faces having to pay an extra £2.44billion a year to the annual EU budget once Britain has left.
Fears for the future of the EU have prompted German government officials to propose that Britain is offered “constructive exit negotiations”.
The aim is of making the UK an “associated partner country” of the EU, according to German newspaper Die Welt today.
Hungarian Prime Minister, Viktor Orban, warned that Europe needs to change its ways.
“Brussels must hear the voice of the people, this is the biggest lesson from this decision,” he told public radio.
“But Europe is strong only if it can give answers to major issues such as immigration that would strengthen Europe itself and not weaken it. The EU failed to give these answers.”
Another critic of the EU, the leader of Poland’s ruling party, said that the UK referendum result shows the need for reform of the EU.