He says the UK could pit nations against each other
European Commission President Jean-Claude Juncker said Britain could divide the EU by making different promises to different member states during Brexit talks.
Speaking to Deutschlandfunk radio Mr Juncker said "The other EU 27 don't know it yet, but the Brits know very well how they can tackle this.
"They could promise country A this, country B that and country C something else and the end game is that there is not a united European front."
Britain are expected to trigger formal divorce talks with the EU by the end of March. Juncker made it clear that as long as Britain are in the bloc, the European Commission is in charge of negotiating trade deals.
Junkcer continued by saying "Now everyone is saying in relation to Trump and Brexit: 'Now is Europe's big chance. Now is the time to close ranks and march together.
"I wish it will be like this, but will it happen? I have some doubt. Because the Brits will manage without big effort to divide the remaining 27 member states."
Mr Juncker said one area where the remaining 27 member states could improve cooperation was in regards to defence. Britain and France are the only EU countries with nuclear arsenals.
Mr Juncker will host US Vice President Mike Pence in Brussels next weekend, and said that a protectionist trade policy by the US would be an opportunity for the EU to forge new trade alliances.
"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."