Premier Li Keqiang had been expected to put a figure on China's contribution to the EU's €315 billion fund at an EU-China summit on June 29, part of Beijing's efforts to become a more advanced economy and not just the world's factory floor.
Li made a pledge to invest in the European fund, which aims to reverse the dramatic fall in European investment since the 2008 global financial crisis, but he created some confusion by also talking about an additional China-EU co-investment fund.
"China wants to invest between €5 to €10 billion initially. The question is how to do it," said one person close to the discussions, who declined to be named.
A second person said the investments would be "in the billions" and added that the goal was to agree on the scheme at a meeting in Beijing in late September between European Commission Vice-President Jyrki Katainen and Chinese Vice Premier Ma Kai.
The Chinese pledge follows decisions by EU governments to join the Chinese-led Asian Infrastructure Investment Bank (AIIB), in defiance of Washington.
One of the obstacles is the design of the EU fund, known formally as the European Fund for Strategic Investments (EFSI), which relies on guarantees that are designed to attract investors by covering any initial losses should a project fail.
If China were to put its money directly into the fund as a guarantee, that would have a multiplier effect by attracting more investment. But under the rules of the fund, China would have no say in choosing the kind of technology projects that Chinese companies could invest in.
China's money could also be lost and need to be replenished if projects fail. For the moment, the fund's guarantees will come from unused funds of the European Union's budget.
Other ways would be to invest in projects chosen by the fund's board, known as platforms, that are defined by the type of economic sector chosen. That would allow China to go into the kind of digital projects they are looking for.
Another option would be to create a vehicle linked to the EU fund, possibly what the Chinese premier was referring to, but that would still need collateral to go to market to issue bonds and raise capital. The EU has little spare cash.