Jean-Claude Juncker is currently acting as caretaker president of the EU executive until December 1, when he is set to pass the torch on to Germany's Ursula von der Leyen.
Juncker, as well as his 27 EU commissioners, will remain in the job until von der Leyen can successfully appoint her own top team.
She is still waiting for Romania to name a suitable replacement after three of her EU commissioner candidates were rejected by the European Parliament.
Britain has also been asked to nominate a commissioner now that its departure has been pushed back.
However, the delays won't hinder the work of the commission and its 32,000 staff, Juncker's spokeswoman Mina Andreeva said.
The executive will restrict itself to current business, only working on files and procedures that are already open, she said.
Exceptions could be made for urgent matters, such as EU responses to international crises.
All work should be done "without pre-empting political choices of the upcoming commission," she said.
During the extra month, Juncker will be undergoing an operation for an aneurysm on November 11, Andreeva announced separately Thursday.
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