The Lisbon treaty rules that decisions by the Council of the EU need 55% of the countries and 65% of the people represented to pass. That gives a group comprising +35% of the population (and at least 4 countries) veto power.

The "Mediterranean Bloc" (France, Italy, etc) comprises more than 35%, so does the "Northern Bloc" (Germany with NL, UK, etc). Post-Brexit the Northern Bloc falls to 30% whereas the Mediterranean grows to 43%. That shifts the power balance in a way the North won't like.

Now, as usual Germany will probably be expected to plug the financial hole Brexit creates. Obviously that won't come without demands for change by the Northern Bloc.