The EU commissioner in charge of the bloc's budget has warned that Brexit will leave a €10bn hole in the EU's finances which will be impossible to fill.
The comments from EU budget commissioner Guenther Oettinger came as the EU warned it might have to impose new taxes to deal with Brexit.
Writing in an EU blogpost, Oettinger said:
Putting a common budget together is no easy matter even at the best of times. In the age of Brexit and the emergence of new priorities such as migration and defence, it closely resembles to squaring the circle.
But, new priorities such as defence and security might mean the "total gap could therefore be up to twice as much".
"We will have to save money because it will not be possible to make up completely for the gap," Oettinger tweeted.
He said the remaining EU27 member states will be split on how to respond to the funding crisis. Net contributing states such as Germany will demand budget cuts, and net beneficiaries from the budget will ask for contributors to pay in more.
In a paper released yesterday, the EU suggested new funding could come from common energy or environmental taxes on companies.