Just when stock-market bulls thought it was safe to go back in the water after Italy’s political crisis stirred a bout of global turmoil, some wary investors and market watchers are ringing alarm bells over Deutsche Bank.

“To this observer (who has consistently warned about Deutsche Bank being the next Black Swan and the imbalances in the European banking system (particularly in Italy)), the risks of a possible negative multiplier effect on other European financial intermediaries and on the region’s economic prospects is profoundly real,” wrote hedge-fund manager Doug Kass in an email to clients Thursday.