The growing literature on credit risk determinants provides results that are based on the set of bad loans present in the bank's assets especially non-performing loans. Besides this classic proxy, the present paper examines the determinants of loan quality deterioration by using a qualitative measure. Actually, we take advantage of a detailed dataset containing information on the quality of loans contracted by banks to different Tunisian firms. The study aims to detect if credit risk determinants are different through quantitative and qualitative proxies. We take into account bank-specific indicators that are likely to affect banking credit risk. Overall, the results show that cost inefficiency and bank profitability are common determinants of the credit risk level and the loan quality deterioration, that are differently influenced by bank size and capitalization.