"We are prepared for all scenarios," a spokeswoman for the European Commission told reporters.
"We have an agreement on the table," she added, recalling a position expressed by President Jean-Claude Juncker. "We will not renegotiate."
Later, UK Prime Minister Theresa May said that the Brexit withdrawal agreement was "the best possible" and "the only possible" deal that would ensure a "bright future" for the United Kingdom.
On 10 December, however, the EU top court has ruled that the UK can change its mind over Brexit.
"In today’s judgment, the Full Court has ruled that, when a Member State has notified the European Council of its intention to withdraw from the European Union, as the UK has done, that Member State is free to revoke unilaterally that notification. That possibility exists for as long as a withdrawal agreement concluded between the EU and that Member State has not entered into force or, if no such agreement has been concluded, for as long as the two-year period from the date of the notification of the intention to withdraw from the EU, and any possible extension, has not expired," the press release read.
The court added that the United Kingdom would have to decide on the cancellation through "a democratic process in accordance with national constitutional requirements" and communicate its decision to the European Council in writing.
The United Kingdom is currently expected to leave the bloc on March 29, 2019.