Spain blocked Monday the appointment of another man to the all-male ECB's executive board but a source said Madrid's decision was motivated by a desire to regain influence at the top of the eurozone's central bank.
Spanish Finance Minister Luis de Guindos, speaking on the sidelines of talks with G20 partners in Mexico, confirmed that Madrid had "rejected" the nomination of Luxembourg's Yves Mersch to the six-seat European Central Bank executive board.
Citing a lack of women candidates, the European Parliament last month voted against endorsing Mersch, even if its support was not legally required, which led eurozone member states to try and confirm the appointment through the back door.
A Monday deadline was set for written objections, but well before its expiry, Madrid intervened.
"The European Council was not today in a position to take a decision by written procedure on the appointment of a new member of the ECB executive board," said a statement issued by the body that groups the leaders of EU member states.
"The issue will be on the agenda of an upcoming meeting in the European Council with the objective of taking the formal decision," the statement added, with decisive summits due on November 22-23 and December 13-14.
"There has been, as you are perfectly aware, a vote in the European Parliament which considered, for a series of reasons, that (Mersch) was not the ideal candidate," de Guindos said.
A Spanish diplomat told AFP that Madrid thinks "there should be a further discussion" among leaders on how to fill the post.
Mersch was named in preference to a male Spanish candidate to replace Spain's Jose Manuel Gonzalez-Paramo and a European source said Madrid was unhappy at what it saw as a "non-transparent" appointment, and that Madrid wants to retain influence at the top of the central bank.
Influence is seen as vital for the Spanish government, which also said on Monday it does not need financial aid from eurozone partners this year, but is still expected on markets to need help.
The ECB would be expected to play a key role in any bailout.
Leaders have already discussed what had become a running sore about a lack of women candidates -- but Spain's decision indicates that wider factors will come into play.
European lawmakers Sylvie Goulard and Sven Giegold said in a statement that they wanted the Parliament's head, Martin Schulz, to ask EU leaders to come up with a new candidate.
The Parliament had already suggested women it would consider qualified to start redressing the ECB's gender balance.
At the summits, unlike the unanimous written procedure, only a majority vote would be required to push through the appointment, meaning Spain could not block Mersch's appointment by itself.
Mersch's qualifications or abilities have not been in dispute. Instead the appointment became a political football with calls for women candidates to be brought forward and complaints that EU leaders were ignoring Parliament.
The last woman on the ECB board was Austria's Gertrude Tumpel-Gugerell between 1998 and 2011.