Fitch downgraded the sovereign credit ratings of Belgium, Cyprus, Italy, Slovenia and Spain on Friday, indicating there was a 1-in-2 chance of further cuts in the next two years.
In a statement, the ratings agency said the affected countries were vulnerable in the near-term to monetary and financial shocks.
"Consequently, these sovereigns do not, in Fitch's view, accrue the full benefits of the euro's reserve currency status," it said.
Fitch cut Italy's rating to A-minus from A-plus; Spain to A from AA-minus; Belgium to AA from AA-plus; Slovenia to A from AA-minus and Cyprus to BBB-minus from BBB, leaving the small island nation just one notch above junk status.
Ireland's rating of BBB-plus was affirmed.
All of the ratings were given negative outlooks.