"Spain will have to make its own decision. It's a matter of sovereignty, but now all tools are available, if there is a demand from Spain," Pierre Moscovici said on a visit to Athens.
EU Finance Ministers will meet in Cyprus on Friday and are expected to discuss concerns of Spain's troubled public finances as well as Greece's efforts to meet tough commitments set by rescue lenders.
Moscovici, who met with conservative Prime Minister Antonis Samaras and top Greece finance officials, said implementation of planned cost-cutting reforms in Athens would determine whether it receives any concessions from emergency lenders.
"This will (to carry out reforms) is strong and the key word is determination," he said. "But what we are now eager to see, what we want to achieve is implementation of this will and that is what we are here to discuss. The rest clearly relies on that."
Athens is seeking more time to ease its debt crisis, arguing that austerity measures will be counterproductive if forced too swiftly on the country's weakened economy.
Rescue creditors are demanding that Greece's conservative-led government slashes a further (EURO)11.
The austerity measures already imposed as part of this bailout deal have held back growth, pushing the country into a three-year recession—triggering a new round of strikes this week.
Government figures released Thursday reveal unemployment in Greece has risen further to 23.6 percent in the second quarter of 2012, up from 16.3 percent the previous year.
Greece's largest labor unions on Thursday called a general strike for Sept. 26 in response to a new government austerity package that is expected to worsen hardship in the recession-hit country.
The 24-hour strike by the General Confederation of Greek Labor will be joined by a civil servants' union.
About 200 disabled people gathered outside the Finance Ministry on Thursday to protest proposed benefit cuts.
"What we are saying is obvious: Blind and disabled people are not to blame for this crisis," Paraskevas Lambrou, a blind man from the central Greek city of Volos, told the AP at the demonstration.
"It is humiliating to be driven into poverty this way," he said.