Bold action is probably at least five weeks away, insiders say, though some more clues may come when the ECB reveals its latest interest rate decision on Thursday.

Several other pieces have to fall into place before the ECB will act decisively, insiders say. These include a request for assistance from Spain, which Madrid is still resisting, a decision by euro zone leaders to let their bailout fund buy bonds at auction, and a German court ruling on the legality of the euro zone's permanent rescue fund, due on September 12.

Above all, ECB President Mario Draghi must overcome the resistance of Germany's powerful central bank, the guardian of monetary orthodoxy, glowering from the other side of Frankfurt.