European Central Bank Governing Council member Axel Weber has told German politicians that Greece may require assistance of up to 80 billion euros ($108 billion) in the coming years.
Weber made the comments to members of Germany's Free Democrats party on Monday, according to people at the event.
The Wall Street Journal also reported that Weber told the politicians that Greece's debt situation was worsening and that "the numbers are changing all the time," the newspaper said, citing a source.
German newspaper Bild said Weber warned that the total amount of aid Greece requires may not be known until later, drawing a parallel with the case of nationalized German property lender Hypo Real Estate in 2008.
The Bundesbank declined to give an immediate comment. Euro zone leaders agreed a giant EU/IMF fall-back aid package for Greece earlier this month. However, the move has failed to quell market concerns.
The premium demanded to hold Greek bonds rather than German benchmarks rose to a euro era record of 482 basis points on Monday.
(One basis point is equivalent to 0.01%, or one-hundredth of a percentage point.)
The cost of protecting Greek government debt against default also hit a record high Germany unveiled further details to the aid plan on Tuesday.
The country's deputy finance minister, Joerg Asmussen, said the euro zone would provide help to Greece in the form of pooled loans, but the idea of buying Greek bonds has been definitively ruled out.
"If it comes to financial aid for Greece, then the path will be a pooled credit, which in the case of Germany would be done via (state bank) KfW," Asmussen told reporters.
"The solution of buying Greek bonds is off the table."
© 2014 Thomson/Reuters. All rights reserved.