Its 2012 annual report describes Manchester United as “an emerging growth company”. Fans of a football club founded in 1878 have always found that amusing. In his nearly 27 years as manager, Sir Alex Ferguson has won 38 trophies. When it listed on the New York Stock Exchange in the summer of 2012, the club had a “global community of 659m followers” – aka fans. Few companies in its particular line of business are as mature as Manchester United.

The term begins to make sense, however, with Sir Alex’s retirement, announced yesterday. More than most businesses, successful football clubs suffer an extreme form of key man risk. In the psychology of football – a sport that manufactures dreams and illusions, not an industry that makes widgets – success and failure embody the personal qualities of the man in charge. That is the manager, not the owner. This risk looms so large at Manchester United that it was among the risk factors in the listing prospectus.

Sir Alex’s successor will have to start from scratch, as all football managers inevitably must. Sir Alex’s tenure has coincided with the death and rebirth of Manchester United – from has-been in November 1986 to a global behemoth valued at $3bn today. Its shares have risen a third since the IPO. It is on target for fiscal 2013 revenue of ￡350m. The route to financial nirvana has been sponsorship, including a deal with insurance company Aon to rebrand its training ground. That followed its $600m, multiyear shirt sponsorship deal with General Motors.