The ECB estimates the euro zone's five largest economies will lose 2% to 4% of their gross domestic product if these measures, ranging from loan guarantees and moratoria to short-time working schemes, are left to expire by the end of 2021.

"The simultaneous termination of policy measures could trigger a protracted downward shift in the recovery path," the ECB said. "Such cliff-edge effects would be concentrated in the first half of 2021."

The ECB cautioned, however, that keeping this support in place for too long could also curb long-term growth and endanger financial stability, by keeping inefficient companies alive and causing capital to be poorly allocated.

"There are substantial short-term risks associated with the withdrawal of policy support, while medium-term risks of protracted policy support should also not be ignored," the ECB said.

(Reporting By Francesco Canepa, editing by Larry King)