Speaking at a conference on the next seven-year budget of the EU, which starts in 2021, Jean-Claude Juncker said it would have to finance joint EU policies in the areas of defence, security, migration, climate change, cohesion and agriculture.
"Britain will be leaving us..., so we need to find ... a means to reacting to the loss of a several billion euros, when a significant contributor goes," Juncker said.
The EU's budget Commissioner Guenther Oettinger said the gap from Brexit would be 12-13 billion euros ($14.4-15.6 billion) per year.
Juncker said that while some EU policies could be reviewed and modernised, EU governments needed to commit more money to the EU budget to finance new areas of joint interest.
"All that cannot be funded from just 1 pct of Europe's wealth," Juncker said. ($1 = 0.8360 euros)