"The Commission on the 19th of December will publish all the information that is generally useful for the preparation of a no-deal [Brexit]," Juncker told a press conference after a European Council meeting in Brussels.
"In terms of future relationship, our UK friends need to say what they want instead of asking us to say what we want," the official also pointed out.
On Thursday, heads of state and government of 27 EU member states, excluding the United Kingdom, held a meeting on the UK withdrawal process.
The summit took place amid difficulties UK Prime Minister Theresa May is facing with the parliamentary ratification of the agreement her team had negotiated.
The European Council said after the EU27 meeting that the Brexit deal reached by Brussels and London was not subject for renegotiation.