MADRID — Spain could ask for a rescue of its struggling banks this weekend when European finance ministers hold an emergency conference call Saturday to discuss the country's financial problems, a move that would make it the fourth member of the 17-nation eurozone to seek outside help since the continent's debt crisis erupted two years ago. The ministers will discuss a potential rescue package for Spain as pressure mounted on the country to prop up the banks hurt by toxic assets after a property boom went bust. A new report from the International Monetary Fund estimated Spanish banks need a recapitalization injection of at least (EURO)40 billion ($50 billion) following a stress test it performed on the country's financial sector.