Josef Ackermann, chief executive of Deutsche Bank and chairman of the Institute of International Finance, the world banking lobby, delivered a stark message last week to Herman Van Rompuy, the European Council president, according to a person familiar with the conversation.

Allowing political indecision to continue into the new year would risk a drastic worsening of the crisis on financial markets, Mr. Ackermann warned Mr. Van Rompuy and other E.U. officials.