"There are serious risks, such as execution risks, given the Greek political situation," Economy Minister Luis de Guindos told parliament in a special session on the deal Greece reached with its creditors, seen as helping it stay in the euro zone.
"This isn't easy - the path ahead is still long and complex," de Guindos said.
In a dig at anti-austerity parties such as Podemos that have gained traction in Spain in the past year, De Guindos took aim at the type of "populist siren songs" which he said had pushed Greece to the edge, under the helm of the leftist Syriza party.
Spain faces a general election around November. The country is due to contribute some 10.1 billion euros ($11.14 billion) of the 86 billion-euro package for Greece.
Germany's parliament is expected to give its crucial approval to the bailout deal on Wednesday.
Some Spanish members of parliament railed against the rescue package, saying it did not benefit ordinary people in Greece, although only 20 lawmakers out of 322 voted against it.
Alberto Garzon, leader of the Plural Left alliance, said the bailout obliged Greece to sell off public assets at knock-down prices and allocated too little to economic stimulus measures.
"If you choose the option of humiliating Greece and obliging Greece to pay until the last drop of blood in financial interest, the economy is not going to recover," he said.
(Reporting by Sarah White; Editing by Tracy Rucinski/Mark Heinrich)
