Singletary is the latest hall-of-fame player to become a head coach in the NFL, and he has some history on his side.
Former NFL hall-of-famers-turned-coaches have had their string run out when they put on a headset and carry a whistle.
Mike Singletary will have to avoid being on this list if he's looking to have longevity and coaching success with the 49ers.
Here's some of the people Singletary must prevent following:
After a brilliant career that included two Super Bowl victories and All-Pro selections, Starr joined the Packers coaching staff in 1972 and then became head coach in 1975.
Starr compiled a disappointing record of 52-76-2 and was dismissed in favor of his former teammate, Forrest Gregg, in 1984.
Starr's Packer teams won no more than eight games during his nine-year head-coaching career.
Gregg was a hall-of-fame offensive lineman for the Packers' Super Bowl teams during the '60s.
Gregg originally began his head coaching career with the Cleveland Browns in 1974. He held that position until 1977.
He spent one year of coaching in the Canadian Football League but came back to the NFL in 1980 with the Cincinnati Bengals.
Gregg had his most success, which included an AFC title in 1981, with the Bengals. He finished his NFL coaching career with the team he played for.
After replacing Starr, Gregg went a dismal 75-85-1 with the Packers from 1984 to 1987.
Even though Ditka has a Super Bowl ring as a head coach with the '85 Bears, he has been fired twice.
Following a 5-11 season in 1992, the Bears fired Ditka. Then Ditka experienced the "three worst years" of his life with the New Orleans Saints from 1997-1999.
Ditka is infamously known for trading all of his draft picks to the Redskins in 1999 to get Ricky Williams. The gamble cost Ditka his job.
He finished the '99 season with a 3-13 record. In his head-coaching career with the Saints, he went 15-33.
Shell was an eight-time Pro-Bowl selection as an offensive lineman for the Raiders. He had two coaching stints with the silver and black.
While the Raiders were in L.A., Shell led the silver and black to a 12-4 season and the AFC West crown in 1990. He took the Raiders to the playoffs twice after that in 1991 and 1993.
However, following a 9-7 season that had Super Bowl hype, as well as a highly publicized rift between him and then-Raider quarterback Jeff Hostetler, Shell would be fired by Al Davis in 1994. Davis later admitted that he regretted that move.
Shell would get a second chance in 2006 with the Oakland Raiders, but the team finished 2-14 and Shell was fired after one season.