Jean-Claude Juncker, the head of Europe's Euro Group, said the currency shared by 17 nations was at a crossroads.
"We have arrived at a crucial point," Juncker said. "The eurozone is at a point where it must prove with, all its means, its determination to guarantee stability," he said.
The Spanish government reported Monday its economy contracted by 0.4 percent in the second quarter from the first quarter with the size of its gross domestic product 1 percent lower than the second quarter of 2011.
In Italy -- another critical economy, the third largest in Europe -- the government sold $5.8 billion in five-year and 10-year bonds. Demand for Italian debt has pushed yields, which represent the cost to the government, down to 5.96 percent from 6.19 percent in late June on 10-year bonds.
For five-year bonds, the interest rate on Italian debt fell from 5.84 percent in June to 5.29 percent.
Juncker's comments followed an upswing in equity markets prompted on Thursday by European Central Bank President Mario Draghi's remark that the bank would do "whatever it takes to preserve the euro."
"We are acting with the ECB. without compromising its independence," Juncker said. "When I say 'we,' that means the Europe Financial Stability Fund.
"It's also to say the 17 governments," he said.