A prominent member of the European Central Bank's Monetary Policy Council is warning about the risks of excessive stimulus and leaving interest rates too low for too long.
The remarks from Jens Weidmann, who also heads Germany's national central bank, come ahead of a crucial March 10 meeting where the ECB will consider ramping up its stimulus.
Mr Weidmann warned that side effects from prolonged periods of easy money and low rates "would be dangerous to simply ignore".
He said long periods of low rates erode bank profits and make it harder for them to pass on the central bank's stimulus to customers.
He also said eurozone governments were not using the breathing space afforded by the stimulus efforts, which are keeping government borrowing costs low, to reduce their budget deficits.
Mr Weidmann is just one member of the 25-member ECB governing council that sets monetary policy for the 19 countries that share the euro currency.
He focused on the impact of low rates on banks, saying that the longer interest costs stay low, the harder it becomes for banks to make money.
Concerns about the health of banks have risen recently in Europe after four Italian lenders needed to be bailed out and major institutions such as Deutsche Bank and Credit Suisse reported large losses for last year.
Banks also must contend with the ECB's -0.3% interest rate on their deposits at the central bank.
The negative rate is an unusual step aimed at pushing banks to lend excess cash rather than hoard it.
Many analysts expect the ECB to cut the rate even further at its next meeting.
Mr Weidmann said it was not the job of the ECB to worry about bank profits in themselves. He said the concern was "rather their capacity to pass on monetary impulses" from the central bank itself. If banks are worried about their finances, they are less likely to lend money to homeowners or businesses.
The ECB is trying to boost inflation that is too low and support a shaky recovery against headwinds such as an economic slowdown in China and emerging markets.
It has cut its benchmark rate to 0.05%, hoping that banks will pass that on to customers in the former of cheaper credit.
And it is buying €60bn in government and private-sector bonds each month with freshly printed money.
That step in theory raises inflation and makes credit more abundant - if banks are in shape to lend.
Annual inflation of 0.4% is well below the bank's goal of just under 2% considered best for economic growth.
The eurozone grew 0.3% in the fourth quarter; unemployment is slowly falling from a high level of 10.4%.