The former prime minister of Denmark, Anders Fogh Rasmussen, speaking at a conference in Copenhagen, said Theresa May's room for manoeuvre in the negotiations would be limited by her lack of a parliamentary majority.
But he added: "It's a statement of common sense that if we are going to radically change the way we work together, we need to get there via a slope, not a cliff edge".
The negotiations have been billed as the most complex in Britain's history as it unravels 44 years of membership and its threat to walk out with no deal in place has anxious European capitals.
SDLP leader Colum Eastwood said the party is meeting Mrs May to aid the process of restoring power-sharing in Northern Ireland.
"We would restore faith in politics if we could show that this parliament can at least function in presenting a view in the national interest which would command a majority on a cross-party basis", said pro-European Conservative lawmaker Ken Clarke.
'What can you say of meaning about such chaos?' the diplomat asked.
"But it's not very strong and stable".
Anxious by immigration and loss of sovereignty, Britain a year ago voted to end its decades-old membership of the 28-country bloc - the first state ever to do so - in a shock referendum result. We will be leaving the single market and by the way, we will be leaving the customs union.
Amid such upheaval, though, there is little agreement on what kind of Brexit May should try for - even assuming she can hold onto her job.
Before the election, May proposed a clean break from the European Union: leaving its single market, which enshrines free movement of people, goods, services and capital, and proposing limits on immigration and a bespoke customs deal with the EU.
Opponents describe that as a "hard Brexit".
As Britain entered a sixth day of political turmoil, May's team continued talks with Northern Ireland's Democratic Unionist Party (DUP) to secure their support in parliament after May failed to win a majority in Thursday's election.
They also said the rally would protest the DUP's record on "access to abortion", and that if the deal goes through the Conservatives would be joining with a party "known to promote policy which restricts the rights of women and LGBT people".
'Everything is all over the place, ' said a senior executive responsible for Brexit preparations at a FTSE 100 company.
The first issue at the Brussels talks will be the status of millions of European Union citizens living in the United Kingdom and British residents of the other 27 countries, including their right to stay, to work, and to access medical care.
But the true figure could be far lower, as the 100 billion does not account for tens of billions that Britain is set to get back in shared assets and rebates.
The situation in Ireland - where the only land border between the European Union and United Kingdom will lie - will also be discussed.
The British government wants the negotiations to include the future relationship with Europe and an all-important trade deal with the bloc.
The EU wants to deal with the first phase of divorce talks before moving on next year to discuss trade, though EU officials acknowledge that the agreements to be reached before Britain leaves can only be concluded as a whole package simultaneously.
The "hardball" European Commission chief negotiator will be across the table from Mr Davis and has already been established as a something of a villain for Brexiteers.