The latest concerns from policymakers comes barely five weeks after the ECB pushed out the timing of its first post-crisis rate hike until 2020 at the earliest amid a period of weakness and uncertainty for the eurozone's economy.

The single currency fell 0.2 percent to $1.128 and also dropped to a day's low against sterling of 86.27 pence .

ECB policymakers think the bank's economic projections are too optimistic as growth weakness in China and trade tensions linger, four sources with direct knowledge of discussions told Reuters.