The economy in the currency region is expected to contract 0.3 percent this year. The commission previously said the region's economy would grow 0.1 percent.
The BBC reported Friday that there is concern that Portugal's economy, currently expected to drop 1.9 percent in 2013, could suffer from a "surprise" downturn after contracting 3.2 percent in 2012.
The commission's forecast is one of several that have undergone downward revisions, the BBC said.
The International Monetary Fund lowered its estimate of the eurozone's 2013 economic performance and says the region will go through a "mild recession" this year.
Similarly, the World Bank in January dropped its expectations for the eurozone economy for 2013.