Richard Parsons has resigned from the CBS Corp board of directors, including his role as interim chairman which he undertook just a month ago following the departure of Les Moonves. Parsons cited health reasons related to his fight with multiple myeloma as the reason for his sudden exit.

The CBS board met this evening and tapped Strauss Zelnick to take over as interim chairman, a decision the board said was unanimous.

“The reason for my departure relates to the state of my health,” Parsons said in the release Sunday night announcing the decision. “As some of you know, when I agreed to join the board and serve as the interim chair, I was already dealing with a serious health challenge – multiple myeloma – but I felt that the situation was manageable. Unfortunately, unanticipated complications have created additional new challenges, and my doctors have advised that cutting back on my current commitments is essential to my overall recovery.

“I trust CBS’ distinguished Board, now led by Strauss Zelnick, as well as CBS’ strong management team led by Joe Ianniello, will continue to successfully guide this Company into its very bright future.”

Zelnick assumes the role immediately. The industry veteran earned a reputation as a media wunderkind, having been named president of 20th Century Fox film studio at the age of 32, and went on to run BMG Entertainment in the 1990s. He is currently CEO and chairman of Take-Two Interactive Software, best known for its provocative Grand Theft Auto game franchise. One of his top priorities will be the board’s search for the next chief executive to permanently replace Moonves, who resigned on Sept. 9 under a cloud of sexual misconduct allegations.

Ianniello has been serving as interim CEO, swiftly fortifying CBS’ executive ranks  as he seeks to prove himself to the board. His recent moves have included promoting Showtime’s David Nevins to a broad chief creative officer role. He also made Showtime’s Christina Spade CFO, Laurie Rosenfield chief people officer, and tapped Dana McClintock to become communications boss after the retirement of veteran Gil Schwartz.

Wall Street could get some insight into CBS’ next steps Nov. 1, when it reports third-quarter earnings and conducts a conference call with analysts. After that its twice-delayed annual shareholder meeting is set for Dec. 11.

Parsons, the Time Warner CEO from 2002-2007, was unanimously appointed to interim CBS chairman in September following Moonves’ resignation amid allegations of sexual misconduct from several women. Parsons had been an advisor to controlling shareholder Shari Redstone as she and her National Amusements holding company navigated a bruising battle with Moonves over control of CBS Corp. The two had developed a close working relationship.

The Brooklyn-bred lawyer Parsons, who also had career stints working for the Rockefeller family and turning around New York’s Dime Savings Bank, is known for his affability and diplomatic skills. After Time Warner he was chairman of Citigroup in the wake of the 2008 financial crisis, and was interim CEO of the Los Angeles Clippers after controversy forced the team’s longtime owner Donald Sterling to resign and sell the team.

Despite Parsons’ reputation as a diplomat, board turmoil continued. Lead independent director Bruce Gordon stepped down on Sept. 25, surprising many observers who saw him as playing an important role in CBS’ next chapter. The Wall Street Journal reported that he quit over the decision to name an interim chairman, a move which he felt would hamper the media company’s ability to attract top CEO candidate who might also want the chairman’s title.

Gordon could not be reached by Deadline to confirm this account.

One person with knowledge of the matter said Parsons health condition, which was well-known to friends, has worsened in recent weeks, forcing him to step down.