"If the UK leaves without an agreement, all measures to protect [EU] citizens and enterprises have already been taken," the French leader wrote on Twitter.
The bloc gave UK Prime Minister Theresa May a clear answer with a clear date of a possible delay of Brexit, and now London must eliminate all ambiguities, he added.
"Europe is a space of peace, prosperity, freedom. Europe is the largest free and democratic space in the world. It should be proud of its model and protect it," Macron stressed.
Addressing the future of Europe, the president noted that it was important to talk about it, including such issues as relations with China, climate, and industrial strategy.
According to various estimates, a no-deal Brexit could cost EU states tens of thousands of jobs and hinder the region's economic growth.
The day before, Macron also commented on Brexit during the summit in Brussels noting that the UK would have to leave the European Union without a deal if British lawmakers reject the Brexit withdrawal deal again next week.
Brexit was originally scheduled for 29 March but UK Prime Minister Theresa May asked the European Union on Wednesday to delay the deadline until 30 June. She refused, however, to follow recommendations to amend the agreement, which has already been rejected twice by parliament.
Prior to that, May promised she would submit a document to parliament in the coming days that would be put to a vote next week. She has continued to consult with political parties about the Brexit deal, but all of them have noted the lack of any progress. Labour lawmakers have refused to participate in the consultations altogether.