Reuters -- A makeshift assistance should be enough to rescue Greece but bigger problems facing Europe would leave the future of the euro currency in question, billionaire investor George Soros said.

Writing in the Financial Times, Soros said what the European Union needed was more intrusive monitoring and institutional arrangements for conditional assistance. He said a well organized eurobond market was desirable.

"A makeshift assistance should be enough for Greece, but that leaves Spain, Italy, Portugal and Ireland. Together they constitute too large of a portion of euroland to he helped in this way," said Soros.

"The survival of Greece would still leave the future of the euro in question."