The single currency slipped to 1.3181 dollars Monday, its lowest level since late September.
It had earlier risen to 1.3281 dollars after debt-ridden Ireland said it will receive an 85-billion-euro package from the European Union and the International Monetary Fund.
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But persistent fears that Spain and Portugal could be the next nations in line to need rescuing hit sentiment.
The euro's direction during later London trade will set the tone for the major currency pairs, Auckland-based HiFX Senior Trader Stuart Ive told Dow Jones Newswires.
"At the end of the day markets are still very, very interested in what's happening with Portugal and Spain as well," he said.
"Whilst Ireland and Irish banks may have settled down, there are still concerns surrounding those other two nations."
