Anderson's family said in a statement Wednesday that they appreciate the support and kindness that friends and fans have shown throughout the Hall of Famer's career and retirement. No further details were released.
The 76-year-old Anderson was inducted into baseball's Hall of Fame in 2000, culminating a major league career that included one nondescript season as a player and an historic run as a manager.
He won 2,194 games as a manager, which was the third-highest total in major league history when he retired, trailing Connie Mack and John McGraw. He now stands sixth, also trailing Tony La Russa, Bobby Cox and Joe Torre. Anderson was the first manager to win World Series titles in both leagues and the only manager to lead two franchises in career wins.
He led Cincinnati's Big Red Machine to World Series wins in 1975-76. He won four National League pennants in Cincinnati from 1970-78, then was fired after consecutive second-place finishes.
Anderson went to the American League and won there, too, directing the Tigers to a World Series title in 1984 and a division title in 1987. He retired after the 1995 season and was added to the Hall of Fame by the Veterans Committee.
"We are very sad to hear the news of Sparky's failing health," Reds owner Bob Castellini said in a statement. "Every day here we are reminded of his contribution to the success of this proud franchise."
The Tigers said they would keep Anderson, his wife, Carol, and their family in their thoughts and prayers.
"Sparky led one of the most beloved teams in franchise history to the World Series title in 1984 and remains the winningest manager in franchise history," the organization said in a statement. "His contributions to the Detroit Tigers remain a significant part of the club's history."