David Montgomery, the Phillies' president since 1997, will take a medical leave of absence from his role as the team's chief executive. Former general manager Pat Gillick will assume Montgomery's duties, the team said Thursday.

The announcement comes at a tumultuous time for the franchise, which will spend $500 million in player salaries over a three-year period without a postseason berth. The future of general manager Ruben Amaro Jr., whose contract runs through 2015, is a constant source of public friction.

Montgomery, 68, underwent surgery to remove cancer from his jaw in May. He has maintained an active presence at Citizens Bank Park ever since — even during chemotherapy and radiation treatments — and helped greet Taney Little League players during a Wednesday pregame ceremony at the ballpark.

The Phillies said Montgomery will return to his duties as the team's chief executive when he is "fully recovered." A team source said this decision did not stem from an ownership shakeup or subterfuge. But Montgomery's stepping aside could soon create permanent change.

In the meantime, Gillick, 77, will handle the day-to-day operations of the entire organization.

"I have the highest regard for David Montgomery, as does everyone in our industry," Gillick said in a statement. "I am glad to be of assistance to the Phillies."

Gillick was not immediately available for comment.

The team's vice presidents will report to Gillick, who could delegate most business matters to various officials, including Mike Stiles, a senior vice president for administration and operations. Stiles, a former United States Attorney, was a classmate of Montgomery's at the University of Pennsylvania.

Montgomery started with the Phillies as a ticket salesman in 1971. He has, since 1997, operated as the team's top executive with complete management authority from the ownership group.

"He's a guy who, in a lot of ways, is our biggest fan," Phillies manager Ryne Sandberg said in May. "From my experience here the last four years, he's the guy who sets the tone as far as it being a family-oriented organization — first-class, the right way. He's the leader of the organization. ... It all starts with David Montgomery."

Gillick was inducted into baseball's Hall of Fame in 2011. He will handle all baseball operations and becomes Amaro's boss. He served as senior advisor to the president and general manager until Thursday, and held a firm place in Amaro's inner circle.

Amaro was one of Gillick's many proteges and succeeded Gillick as general manager after the 2008 world championship. Montgomery, with influential input from Gillick, chose Amaro over Mike Arbuckle, another longtime Phillies executive.

Montgomery, in a June interview with The Inquirer, endorsed Amaro as general manager despite the team's continued failures.

"I think we have pretty good people doing these jobs," Montgomery said. "We saw, over a long period, pretty good success with this group of people. Obviously, Ruben is part of that group."

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