Brussels said the three countries would see two negative quarters of economic growth in a row, which is the technical definition of a recession.
In its latest economic forecast, the commission also downgraded its outlook for eurozone growth again.
It said the 15-nation euro bloc would now grow by 1.3% this year, against previous projections of 1.7%.
Earlier this month, data showed the region's economy shrank by 0.2% between April and June - the bloc's first decline since its creation in 1999.
The contraction was driven by a slowdown in exports and consumer spending.
But high inflation in the region led policy makers at the European Central Bank to keep interest rates at 4.25% at its latest meeting, allowing no relief for the eurozone's slowing economies.
In its latest report, the commission believed that inflation was now likely to creep up to 3.6% in the eurozone - above its previous predictions of 3.2% and way above the government's target of 2%. ...