SAO PAULO A top executive of Casas Bahia has decided to quit after less than five months on the job, deepening a corporate crisis that has seen shares in one of Brazil's largest retailers plummet this year.

Casas Bahia, formerly known as Via, said in a securities filing late on Tuesday that Commercial and Operations Vice President Abel Ornelas Vieira had handed in his resignation from a role he had assumed in early May.

Vieira's departure comes as the company struggles to convince markets it will make it out of a restructuring process after an unsuccessful share offering earlier this month prompted investor concern about the firm's financial health.

Shares of the retailer were up 1.5% on Wednesday, but have plunged more than 40% since Sept. 14, when it announced the offering had been priced at a 28% discount over the previous day's closing, falling short of its own expectations.

JPMorgan analysts said Vieira's departure did not come as a surprise given the challenges faced by the company both on the operating and balance-sheet sides. They noted that he was Casas Bahia's only officer with extensive retail background.

Vieira had been an executive at Casas Bahia for the past four years, after also serving as the company's vice president of executive operations between 2010 and 2013. He had also worked at Magazine Luiza and Walmart.

"We expect shares to remain under pressure, particularly now that a new commercial head is likely to be appointed in the midst of a challenging turnaround process," JPMorgan added in a note to clients.

Casas Bahia last month announced a series of restructuring measures, including shrinking inventories and closing stores.

The company said CEO Renato Franklin will tap another executive for the job on an interim basis until the board of directors can vote on a replacement for Vieira.

($1 = 5.0249 reais)

(Reporting by Paula Arend Laier; Writing by Gabriel Araujo; Editing by Bill Berkrot)