In a letter to European Central Bank and International Monetary Fund leaders dated 6 June, Mr Schaeuble said a new package was needed.
He suggested a bond swap to give Athens more time to repay its debts.
A 110bn euro (£161bn; £98bn) Greece bail-out package was agreed last year.Burden sharing
"The situation is difficult," Mr Schaeuble wrote.
"A return by Greece to the capital markets within 2012, as assumed by the current programme, seems more than unrealistic. This means the volume of the current programme is insufficient to cover Greece's financial needs. (read more)