The grocery chain Kroger said on Monday that its chief executive, Rodney McMullen, resigned after a board investigation of his personal conduct.

Mr. McMullen’s conduct was not related to the company’s financial performance or its operations, Kroger said in a news release, but it was “inconsistent” with the company’s business ethics policy. His actions did not involve any Kroger workers, the company said.

The management change comes as Kroger, which has headquarters in Cincinnati, has been dealing with the fallout from its collapsed merger with the grocery chain Albertsons.

Kroger said its board learned about “certain personal conduct” of Mr. McMullen’s on Feb. 21 and immediately sought outside counsel to lead an investigation. It said the actions in question were “unrelated to the business.”

The company appointed Ronald Sargent, its lead director, as interim chief executive while the company searches for a replacement. He also took over Mr. McMullen’s role as chairman. Mr. Sargent has been a director at the company since 2006 and said that he had spent summers in college working at its stores.

“I plan to be a steady, but active, hand in the execution of our strategy,” Mr. Sargent said in a statement.

Mr. McMullen had worked at Kroger for more than four decades. He started in 1978 as a part-time stock clerk in Lexington, Ky., was elected to its board of directors in 2003 and was appointed chief executive in 2014. He was named chairman in 2015.

Kroger announced the management shake-up days before the company reports its fourth-quarter earnings on Thursday.

The last few months have been a tumultuous time for Kroger. After federal and state regulators blocked Kroger’s $25 billion bid for Albertsons in December, Albertsons sued Kroger. The deal would have been the biggest grocery store merger in U.S. history and would have created a $200 billion company with 5,000 supermarkets across the country.

The Federal Trade Commission sued to halt the deal, arguing that it would reduce competition and raise prices at the expense of workers and consumers. Judge Adrienne Nelson of the U.S. District Court in Oregon sided with federal regulators and a state court in Washington blocked the deal in a ruling made about an hour later.

The next day, Albertsons said it had backed out of the merger and filed a lawsuit seeking billions of dollars in damages against Kroger, accusing it of not using its “best efforts” to secure approval from regulators. Kroger has disputed Albertsons’ claims.