Richard D. Parsons, a longtime media executive who less than a month ago was named the interim chairman of CBS to help stabilize the company, said on Sunday that he was stepping down because of illness.

Forced again to reshuffle its leadership ranks, the CBS Corporation named as his replacement Strauss Zelnick, the head of the video game publisher Take-Two Interactive Software. Mr. Zelnick, who is widely respected within the media industry, was appointed to the CBS board in early September. He had led the music publisher BMG Entertainment and had served as president of 20th Century Fox.

The shake-up complicates an already difficult time for CBS, which has spent most of the past year fighting scandal on multiple fronts. Several accusations of sexual misconduct were made against Leslie Moonves, its chief executive, as well against a longtime leader of its news division. Separately, a contentious legal showdown with its controlling shareholder threatened to upend the company’s management.

As CBS worked to resolve the disputes, Mr. Parsons was instrumental in negotiating the departure of Mr. Moonves. He also advised on appointing Joseph Ianniello, the chief operating officer, as acting chief executive, and helped install six new directors to lead the company out of trouble, according to several people close to the board who spoke on the condition of anonymity. The lawsuit was dissolved as part of Mr. Moonves’s exit agreement.