In an interview with ARD public television, Schäuble insisted on waiting for the results of an examination of Greek public accounts next month before deciding if new measures were required.
But if they prove necessary, "a central point will be avoided (...) to relieve private creditors at the expense of the taxpayer".
"We must have a clear rule: if there is a rescheduling (of the debt), all credit must be rescheduled," he said.
Officials from the EU, the IMF and the European Central Bank are examining Greek finances and the progress of an austerity programme imposed as a condition of last year's international bailout. They will report back in June.
The €110 billion rescue in spring 2010 was the first of three European rescues, followed by Ireland and Portugal.
However, a severe recession has complicated Athens' efforts to bring its finances in order.
Greece was expected to return to the financial markets next year but it appears unlikely and there is speculation that it will need further financial assistance.
The German daily Die Welt reported Saturday that the EU Commission, the IMF and Germany were calling for Greece to reschedule its massive debt burden, due to a deteriorating situation.
Citing unnamed sources, Die Welt said the International Monetary Fund (IMF), the European Union executive arm and the government in Berlin believed prolonging the repayment terms on some loans to Greece has become the least worst option to save the country from defaulting.
However the European Central bank and France remain opposed to any such debt restructuring, the article added.
EU Commission spokesman on economic affairs Amadeu Altafaj dismissed the report as "absurd".
"A restructuring of Greek debt is out of the question," he told AFP.
Speculation has mounted in recent days that Greece will need an additional €60 billion over the next two years as it won't be able to return to financial markets next year as expected to re-finance its massive debt.
Eurozone and EU finance ministers are expected to discuss Greece at meetings on Monday and Tuesday.