Pablo Hernandez de Cos, a member of the ECB's governing council, said ECB should consider retaining some of the flexibility in its emergency bond purchase programme as it transitions to other asset purchases after COVID-19 's crisis.

The Spanish central bank governor said on Tuesday that the "main lesson" from the plan was that shifting purchase preferences to areas in the economy that were most needed could significantly improve the effectiveness and efficiency of purchases.

"therefore, it is desirable to retain some flexibility when discussing our future purchase plans," he said.

The 1.85 trillion euro ($2.2 trillion) epidemic-prevention bond-buying program is particularly strong and has been used to drive down borrowing costs in heavily indebted Italy and other hardest-hit areas. It is also clearly temporary and is scheduled to end at the end of March 2022 or after the management committee judges that COVID-19 's crisis is over.

Christine Lagarde, president of the European Central Bank, said this month that the plan could be "transformed into a new format".

Hernandez de Cos is considered to be one of the dove members of the management committee. He said it was "too early" to say when to start discussing post-crisis measures.

But he also said the ECB decided last week to change its guidance on future policy, suggesting that adjustment measures would boost inflation.