(Adds comment from campaign manager)
By Luke Baker
BRUSSELS, June 11 (Reuters) - The manager of Jean-Claude Juncker's campaign to become the next president of the European Commission has accepted a job with an international financial organisation in London, raising questions about Juncker's candidacy.
Martin Selmayr, a senior Commission official who took unpaid leave to run Juncker's election campaign, has been appointed EU director at the European Bank for Reconstruction and Development, the Commission said on Wednesday.
Selmayr, a German lawyer who rose rapidly up the Commission ranks, was expected to become chief of staff for Juncker if his Commission bid is successful.
Juncker, a former prime minister of Luxembourg, remains very much in the running for the job, but Selmayr was regarded as a sharp operator and his departure will be seen as a blow.
In comments posted on Twitter, Selmayr sought to play down any such interpretation of his job announcement.
"You really think Juncker needs me to win? Believe in democracy!" he said, adding: "(Juncker) will be next ComPresident, i.e.: I'll work for him wherever I'll be located."
Selmayr's new appointment could also be seen as a move to ensure he retains a position in the Commission, where a vast number of jobs will change in the coming months.
He has already been appointed an adviser in the Commission's economic and financial affairs department, a role he will take up from July 1. The EBRD appointment is effectively a secondment from that post and does not prevent him taking up a job with Juncker if the Luxembourger does get the Commission presidency.
British Prime Minister David Cameron has led opposition to Juncker, 59, describing him as a old-style federalist and not the sort of modernizing influence Europe needs to overhaul how the Commission works.
While Juncker has been chosen by Europe's centre-right political group as their candidate for the Commission, it is up to EU leaders to nominate him. He would then have to approved by a majority in the European Parliament.
EU leaders will meet at a summit on June 26-27 to discuss who to nominate, with Cameron determined to rally support to block Juncker's candidacy. German Chancellor Angela Merkel has resolutely supported Juncker's bid.
If Juncker does not end up being appointed to the Commission it is possible that he will be named as president of the European Council, a critical role that involves chairing EU summits and coordinating the policy positions of EU leaders. (Editing by Ralph Boulton)