Mrs Merkel yesterday restated her support for Jean-Claude Juncker as the Commission's next president, following an overnight summit with Mr Cameron and the leaders of Sweden and the Netherlands at the Harpsund country residence of Swedish PM Fredrik Reinfeldt.
Speaking alongside the other leaders at a press conference concluding the summit, Mr Cameron made clear it would be "very unhelpful" to his plan to campaign for Britain to stay in the EU in a referendum in 2017 if the former Luxembourg Prime Minister becomes the Commission's most senior official.
Appointments to the EU's top jobs when the current Commission steps down in October must ensure that the 28-nation bloc is put "firmly on the path of reform", he said.
But the issue of the presidency was put on hold for now, as Mr Reinfeldt said that all four leaders had agreed that "the future policy priorities of the European Union must be decided before we can decide on appointments to different top jobs".
Asked about reports that Mr Cameron had privately warned her that a presidency led by the federalist Mr Juncker would make the UK's exit from the EU more likely, Mrs Merkel said: "I made myself clear by saying that I am for Jean-Claude Juncker.
"But when I made that statement in Germany I also made the point that we act in a European spirit. We always do that."
Mr Cameron's official spokesman said that the Harpsund summit had demonstrated agreement among the four leaders on "the need for reform of the EU", and insisted it was "not at all" the case that the Prime Minister had come away from Sweden with nothing because no breakthrough had been made on blocking Mr Juncker's presidency.