BRUSSELS — Where will the money come from? This is the contentious question that the EU needs to answer every seven years — and this time around, the issue is even more complicated.

The U.K., which has been one of the EU's key contributors, left the bloc on January 31. Over the last few years its net contribution to the EU has been around £7.8 billion per year and, as such, the U.K.'s departure could leave the group with a shortfall of around £55 billion ($71.3 billion) over the next seven years.

The remaining 27 EU countries are now scratching their heads and trying to find ways to make up the difference. In an emergency meeting Thursday, the bloc's leaders will seek to agree on its next budget, but there are expected to be long and arduous fights between those paying the highest amounts to the EU and those receiving the most money from it.

"The situation won't get better over time ... We face between 60 and 75 billion (euro, $64.7-81 billion) gap because of Brexit, we are facing new challenges and new priorities ... and member states have a tight budgetary situation, so realism is needed," an EU official, who did not want to be named due to being close to the negotiations, told reporters in Brussels Wednesday.

The EU's budget is used to finance policies across the bloc, ranging from developing rural areas, security and the promotion of human rights. However, EU countries have a hard time figuring out how much money to allocate to the different policy aims.

There are 15 nations that do not want a smaller budget, including countries such as Portugal, Poland, Spain and Greece. This group has been dubbed the Friends of Cohesion, as it opposes cuts to the so-called Cohesion funds — which support members whose gross national income per inhabitant is less than 90% of the EU average.