Mrs Merkel is running for her fourth term at the helm, which polls suggest she will win comfortably.
But Mr Juncker’s chief of staff, Martin Selmayr, warned the proposals could be seen as “too German”.
On the back of Mrs Merkel’s pitch, he issued words of warning that the rose-tinted vision of an integrated Europe may not be everyone’s cup of tea.
Speaking with bankers on Tuesday, he said: “The future of Europe will be very lonely… if we go in this debate too German.”
He said the powerhouses of Europe should avoid acting like “legal robots” when it came to the impact of financial and economic governance on citizens.
And his word of the night was “compromise”, which he explained as: “Something at EU level that creates a stronger sense of belonging, that contributes to more equality between our member states, to more convergence between our member states.”
Mrs Merkel and Mr Macron are attempting to put on a united front in the wake of Brexit, reaffirming the European project is as strong as ever and renewing ties in a bid to quell any dissent.
Soon after Mr Macron’s election victory, which he won running on a pro-European ticket, the leaders drew up their plans for further EU integration.
Referring to the idea of a European Monetary Fund, Mrs Merkel said: “It could make us even more stable and allow us to show the world that we have all the mechanisms in our own portfolio of the eurozone to be able to react well to unexpected situations.
“I could also imagine a (combined) economy and finance minister.”
And Mr Macron echoed her sentiment, saying: “This is a revamp that we need.”
The fresh proposals which have fleshed out are due to be formally announced on September 24, soon after Germany’s election.