Francois Perol said on the sidelines of an economic conference in Italy on Saturday that negative interest rates in the eurozone are a major problem, squeezing interest margins in a way that was unsustainable over the longer term.

"I am much more worried than I was in 2009 in certain respects," Perol said outside the closed-door conference, held on the shores of Lake Como.

"It was 100% clear what had to be done (in 2009)," he added. "I think it's more of a difficult situation for banks (now) because fundamental changes are underway in an environment that's incredibly challenging due to negative interest rates."

Perol's comments on negative rates are among the strongest from a big eurozone bank since the European Central Bank sent its deposit rate a little deeper into negative territory last month, in an effort to prod banks harder to increase lending.