Last week, Martin Selmayr, secretary-general of the European Commission, has briefed ambassadors about the plan, according to diplomats.
"He said that five days is all the time they need for most of it," a diplomat told the Financial Times.
The European Commission’s accelerated method for passing legislation, which was explained to member states, will permit the the EU to prepare for a worst-case scenario without undermining negotiations with the UK on a withdrawal deal.
The EU hopes to strike a deal with the UK where transport, customs and financial services are seen as priority areas. In case of a "no-deal", Brexit temporary failsafes are likely to be needed to prevent chaos.
Should it be used, the five-day plan would control how EU institutions and member states should prepare and how to mitigate the worst effects of Brexit.
Such an approach is potentially controversial, however, because it would concentrate power in the hands of the commission, while limiting the input of member states or the European Parliament. Some EU diplomats are also doubtful that all necessary rule changes could be achieved through such a fast-track approach.
English Edit: Lisa Castey Hall Nielsen