Three of Spain's healthier lenders, including top player Santander, are expected to show the scars from a tough economy when they report first-quarter earnings on Thursday.
Recession in its home country and low interest rates are likely to weigh on Santander's net interest income, which broadly measures lending margins.
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The euro zone's largest bank is expected to post a 1.3 billion euro ($1.7 billion) net profit, down 17.2 percent on a year earlier, according to a Reuters poll of analysts, as income from key markets such as Brazil also drops.
Spain's third-biggest lender Caixabank and Sabadell, the fifth, are also expected to report operating profit knocked by restructuring expenses from acquisitions.
They recently bought some of state-rescued banks whose exposure to soured property loans and assets forced Spain to seek a 41 billion euro ($53 billion) bailout for its weak lenders last year.
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Santander, Caixabank and Sabadell managed to survive without government help, though their 2012 earnings were also gutted by heavy provisions on rotten real estate deals.
Attention is now turning to troubled loans in other segments, including small company borrowers.
Spain's biggest state-rescued lender Bankia said late on Wednesday that its bad debts rose to 13.1 percent at the end of March, well above February's sector average of 10.39 percent, as it managed to swing back to profit from record losses.
Quarterly net profits at Caixabank and Sabadell could be boosted by accounting gains derived from acquisitions at knock-down prices, but Sabadell's profit is expected to drop 82 percent to 14.7 million euros, according to a Reuters poll of eight analysts.
The average of three analysts' predictions for Caixabank first-quarter net profit was a more than threefold increase to 171 million euros against a year earlier.
At Santander, investors will also be looking out for revenues projections in Latin America, which contributes about 50 percent of group profits, and for signs of progress with planned share listings for its UK subsidiary and U.S. consumer finance business to raise capital.