Spanish Economy Minister Nadia Calvino, who narrowly lost a vote to become Eurogroup chief, said on Friday that one minister did not keep his pledge to support her.
"We had ten votes secured. Someone didn't do what he said he was going to do," Calvino said in an interview on radio station SER. "The vote is secret and, in this case, remote."
She declined to say who she thinks the person was.
The Eurogroup of euro zone finance ministers on Thursday elected Irish Finance Minister Paschal Donohoe as its new chair after two rounds of votes. Donohoe defeated Calvino by one vote.
Calvino had secured the support of France, Germany, Italy and Portugal. The countries supporting her represented more than 80% of the euro zone population and economies, Calvino said on Friday.
Unlike Calvino, Donohoe, has in the past taken a strong stance against government spending increases and deficits.
He also opposes a potential EU tax on digital firms, while Calvino and the Spanish government are staunch advocates of the tax.
"The vision of Europe that country has, doesn't match the one we have," Calvino said.