Downing Street has insisted that the race for European Commission president remains open, after former Luxembourg PM Jean-Claude Juncker announced that he was "more confident than ever" that he will land the job.
Federalist Mr Juncker made his prediction in a message on Twitter just days after Prime Minister David Cameron made clear his opposition to his appointment.
Meanwhile, Mr Cameron's spokesman declined to comment on speculation that IMF chief Christine Lagarde was being touted for the job, which is generally offered to a candidate able to secure consensus support from leaders of the EU's 28 member states meeting in the European Council.
An unconfirmed report by news agency Reuters claimed that German chancellor Angela Merkel privately raised with French president Francois Hollande the possibility that he might put Ms Lagarde's name forward.
Mr Cameron has reportedly clashed with Mrs Merkel over her support for Mr Juncker, whose candidacy is backed by the European People's Party (EPP) grouping to which her CDU party belongs in the European Parliament.
But Downing Street has declined to say which candidate would have the PM's support, insisting that his focus is on ensuring that the new European Commission, which comes into office in October, has the right priorities to restore EU competitiveness and cut red tape.
At a European Council summit in Brussels last week, Mr Cameron warned that the new Commission president must be someone willing to confront perceptions that Europe had become "too big, too bossy and too interfering" in the wake of the success of anti-EU parties in European elections across the continent.
But Mr Juncker has received indications of support from a number of European leaders, including Mrs Merkel, and today tweeted: " I am more confident than ever that I will be the next European Commission President."
Responding to the message, Mr Cameron's official spokesman said: "In terms of candidacies and the like, the Prime Minister's view has not changed.
"People will put themselves forward for senior roles. I don't think there's anything to be surprised about around that. But in terms of the process, it is the one that the European Council was discussing last week. There is a role for Herman van Rompuy, the president of the European Council, to undertake the consultations that are under way."
The PM, who last night spoke to Spanish premier Mariano Rajoy by telephone about the upcoming appointment, was not voicing public support for any individual at this stage, said the spokesman.
Asked whether he was pleased to see the name of Ms Lagarde - a former French finance minister - being discussed, the spokesman said: "His approach is to focus on the priorities for the European Commission and for there to be candidates who, as he said in Newark earlier this week, 'get that'.
"The key is that we have a European Commission going forward that is focused on the importance of reform. That is the thrust of the approach he is going to continue to take."
Mr Cameron's approach appears to have won backing from former EU trade commissioner and Labour peer Lord Mandelson, who said it was "reasonable" for the Prime Minister to demand that a range of candidates are considered.
Lord Mandelson said Mr Juncker was qualified for the job but insisted a "wider and informed choice" of candidates must be drawn up.
He told BBC Radio 4's Today programme: "He may or may not be the nightmare candidate. I'm saying that he should be considered among others.
"I think it is reasonable that the Prime Minister argues for making an informed choice from a range of candidates."
Lord Mandelson backed Ms Lagarde or Pascal Lamy, former director general of the World Trade Organisation, for the top job.
But he dismissed suggestions that former prime minister Tony Blair could vie for the post.
"Tony has ruled himself out for any top job," he said.
" He's been pretty clear in saying he wants the best candidate for the job, he doesn't want the job for himself."
Lord Mandelson said it was a "shame" that Mr Blair had been lost to national politics but his interventions were " acute " and "always worth listening to".
"I'm sure Tony Blair will have many contributions yet to make."