Rating agency Fitch Ratings on Friday affirmed Portugal's sovereign debt rating at 'BB+' but downgraded the outlook to 'stable' from 'positive'. The agency noted that the downward revision of the outlook was driven by the bigger-than-expected fiscal deficit.

"Fiscal performance was well off-target in 2015, with the general government deficit at an estimated 4.2% of GDP compared with the 2.7% initially expected," Fitch said.

"The government's plans for fiscal deficit reduction in 2016 are also at risk," the agency added.