Fred Hutchinson was manager of the Cincinnati Reds in 1964. He missed time while battling cancer first leaving on July 27. He returned August 4th but left again 9 days later, with coach Dick Sisler in charge. I think Sisler was interim manager. Hutchison formally resigned on October 19th and died three weeks later.
Detroit Tigers had two managers who got sick and died in 1966, although they had interim managers in place. Charley Dressen, who missed the first two months in 1965 because of a heart attack, suffered a second coronary on May 16, 1966. Recovering from this, he suffered a kidney infection and died of cardiac arrest on August 10th. His replacement, Bob Swift, managed for two months and was hospitalized with what was thought to be food poisoning but was later diagnosed as lung cancer. Frank Skaff took over, with Swift dying on October 17th.
Gil Hodges, Mets manager, died of a heart attack during spring training on April 2, 1972 which was the second day of the first ever baseball strike
Nitpick: Bobby Charlton was never England manager. He was captain once (as far as I can tell, for his 100th cap), unlike compatriot Bobby Moore with whom he played in England’s World Cup win 50 years ago (almost to the day). You may be confusing him with Bobby Robson, who was England manager 1982-1990.
On topic, it’s not American sports but Gary Speed committed suicide while manager of the Wales national football team.
2 others in the Big Ten: Dave McClain, Wisconsin’s head football coach, died of a sudden heart attack in the spring of 1986. Terry Hoeppner of Indiana was diagnosed with brain cancer after his first season in 2005. He coached the team in 2006, missing some games to address the cancer, then died in the spring 2007 while he was officially on “medical leave” and a new interim coach had already been decided on.