Prolonged low growth is the biggest risk facing the euro zone, European Central Bank Governing Council member Ewald Nowotny said on Friday, while refusing to rule out a U.S. Federal Reserve-style quantitative easing (QE) program for the region.
"I think that we have all learned in life that we should never say 'never'," Nowotny, who also heads the Austrian central bank, told CNBC when asked about the possibility of QE.
Read MoreQuantitative Easing: CNBC Explains
The comments were surprising given Nowotny's generally hawkish policy stance. He reportedly sided with Germany's Jens Weidmann in voting again the ECB's asset-backed securities purchasing program, which was announced in September.
Nowotny declined to comment on this on Friday, and also refused to rule out expanding the purchases to include corporate bonds—or even government debt purchases.
"We have now just started some new programs. I think we should take time to look at the effects," he said.
Global stock markets wobbled on Wednesday and Thursday after the Fed took a surprisingly hawkish tone as it confirmed the end of its bond purchases. Nowotny said the move would have little impact on Europe, however, particularly with regards to capital flows.
The policymaker added that sustained low economic growth was a more likely threat to the euro zone than flat growth or even economic contraction. Official estimates indicate the euro zone economy flatlined between April and June this year, after growing by 0.2 percent in the first quarter.
"I think this is the biggest challenge we face right now," said Nowotny.
In addition, he agreed that the euro might continue its sharp depreciation, describing this as a "side effect" of ECB stimulus measures.
"If you look at in a historical context, of course there is potential," he told CNBC. The euro has declined around 6 percent against the dollar since its 2014 peak in June.