Mario Draghi may have skipped the Federal Reserve's Jackson Hole symposium this year, but he can't dodge its conclusion: Central banks can't steer inflation as well as they thought.

Less than six months into a stimulus program that the European Central Bank (ECB) president promised would revive consumer-price growth, the euro area is facing renewed disinflationary pressure as China's economy slows and commodity prices slump. Inflation failed to pick up this month, data showed on Monday, and Draghi may have to downgrade the institution's forecasts on Thursday.

The newest risk to prices highlights how headline inflation in the 19-nation currency bloc—as in the U.S., the U.K., and other industrialized nations—is still far below target, even as the economy recovers. Whether that heightens calls for the ECB to step up its 1.1 trillion-euro (US$1.2 trillion) quantitative-easing program will depend on how Draghi communicates the complex economic picture.