IMF chief Christine Lagarde has said she is not in the race to be the next president of the European Commission.
Ms Lagarde said she intends to see out her five-year term as boss of the world's financial watchdog, adding: "I am not a candidate. I have a job."
The possibility of Ms Lagarde taking the job had reportedly been discussed by German Chancellor Angela Merkel and French President Francois Hollande.
The UK has made clear its opposition to frontrunner Jean-Claude Juncker.
Shortly before joining Ms Lagarde at an IMF press conference in London, Chancellor George Osborne underlined the UK's view that whoever heads the European Commission must understand "the need for change" and not ignore the EU's "weak" economic record and the anger shown by voters in recent polls.'Desperate' attacks
Asked at the press conference if she would consider leading the Commission after current president Jose Manuel Barroso steps down in October, Ms Lagarde said she intended to see out her term at the IMF, which ends in 2016.
The BBC's Chris Morris writes: Luxembourg's Jean-Claude Juncker is officially "more confident than ever" that he will get the job, but efforts by his supporters to present victory as a fait accompli have been stopped in their tracks. EU diplomats close to Mr Juncker admit that some countries are sceptical, but they insist that only one - the UK - is openly opposed to their man. He could still win, but it won't be easy.
"On this EU thing, I am not a candidate," said the former French finance minister.
"I have a job, I happen to think it is a rather important job and I intend to complete my term."
Mr Juncker, the former prime minister of Luxembourg, has the backing of the German chancellor.
The decision on who will lead the EU's executive body has become increasingly acrimonious, with Mr Juncker accusing the British media of seeking to sabotage his candidacy and making "desperate" attacks on him.
"I don't give interviews" - Jean-Claude Juncker refused to answer the BBC's questions on Thursday
As the preferred candidate of the European People's Party, the centre-right grouping which won the most seats in last month's European Parliament elections, Mr Juncker is in pole position to take the key job.Public anger
But several countries, including the UK, Sweden and Hungary, are unwilling to support him, feeling that he is not a dynamic reformer and has an unswerving belief in closer political union between EU member states.
Other candidates in addition to Ms Lagarde have been touted - including ex-WTO boss Pascal Lamy - although opponents of Mr Juncker have not coalesced around a single individual.
Asked about the UK's stance on BBC Radio 4's Today programme, Mr Osborne did not mention Mr Juncker by name and said he would not discuss individuals.
But he said: "We need people running these European institutions who clearly understand the need for change. We have just had European elections where, not just in this country but across Europe, people said very clearly they were not happy with how Europe was working.
"Anyone who wants one of these important jobs in Europe and they affect all of our lives, needs to demonstrate, in my view, that they understand people's anger at what has gone wrong in Europe and understand the need for change in Europe."
Mr Osborne said the slow recovery of much of the eurozone from the recession, in contrast with the UK's faster growth, showed the need for new thinking in Brussels.
He added: "Britain is seeking change for Europe's sake, not just Britain's sake... we have got to have a response across Europe to the election results, the weak economic performance, we have got to have change in Europe."
Ms Merkel, who has given Mr Juncker her public backing, discussed the issue with Mr Cameron on the fringes of a meeting of G7 leaders in Brussels on Thursday.
However, he is also said to have indicated his willingness to negotiate.
EU leaders traditionally choose the Commission head on their own, but under new rules have to "take into account" the results of the European elections.