The European Central Bank may discuss technical changes to its asset-buying scheme next week but a decision could be deferred until December when the bank will also decide whether to extend the scheme beyond March, sources familiar with the discussion have said.

Compromise proposals could include relaxing, on a temporary and partial basis, a rule forcing the ECB to buy debt in proportion to the size of each euro zone economy, the sources familiar with the discussion added.

That could potentially reduce the ECB's purchase of German debt, risking renewed conflict with Berlin, which has already argued that the ECB is subsidising indebted countries.

Other proposals may include buying a limited amount of bonds yielding less than the deposit rate, which the ECB currently rules out, and buying a bigger share of any individual bond issue, the sources added.

The ECB is looking for ways to ensure it can continue buying €80 billion worth of bonds every month even if it decides to extend the programme beyond its current end-date in March.

The asset purchase scheme was launched in March 2015 as part of efforts to revive growth and inflation in the euro zone.

But because technical changes will depend to a great degree on whether the scheme is extended, many policymakers advocate combining the two decisions, probably in December, the sources told Reuters.

"Let's not get too far ahead of ourselves," said an ECB rate-setter who tends to vote with the majority.

“The technical changes are closely related to the policy change and should be made together."