European Commission President Jean Claude Juncker dismissed the possibility that he will seek a second term, in an interview to be aired on Sunday on German radio station Deutschlandfunk. "They could promise country A this, country B that and country C something else and the endgame is that there is not united European front"'.
Mr Juncker said one area where the remaining 27 member states could improve cooperation was in regards to defence.
European Union member states are becoming even more divided over opinions that "are not necessarily compatible", he said, referencing Hungary and Poland. You have to create a fundamental consensus again.
"While we're negotiating with the British, we have to agree on the definitive visions for this continent if we want to avoid an apocalyptic mood", Juncker said.
The Brexit Department declined to comment directly on Mr Juncker's remarks, but pointed to a recent speech by the Prime Minister in which Mrs May said she wanted a "strong and constructive" partnership with the EU.
Mr Juncker reiterated that Britain can not negotiate trade deals as long as it remains in the European Union....
"It would be a change that we have to use, and we should not allow the Brits to pursue trade deals now with others because they are not allowed to do so".
Juncker, who was elected in 2014, made the announcement on German radio.
The European Commission is responsible for proposing new EU legislation, drawing up the EU's budget and supervising EU funding.
The European Commissioner is not elected by popular vote, but rather a majority of the 751-member European Parliament. During his tenure as Luxembourg PM, Juncker also headed the Eurogroup of eurozone finance ministers from 2005 to 2013.