Manchester United shares slip on Alex Ferguson news
The opening bell on Wall Street saw shares down by 3pc, driven lower by worries over whether the club can appoint the right replacement for the most successful manager in English football history.
His successor will be the key figure at a business laden with almost £370m of debt and tightly controlled by its US majority owners, the Glazer family.
The club, which trades under the MANU ticker on Wall Street, announced his departure while US markets were closed, but shares slipped on opening as investors digested the impact of the 71-year-old's departure on one of sport's most successful franchises.
In the prospectus to its 2012 stock market flotation, Manchester United warned: "We are highly dependent on members of our management, coaching staff and our players.
"Any successor to our current manager may not be as successful as our current manager."
Shares in the club have surged 34pc since floating in August at $14 dollars per share, closing on Tuesday evening at $18.77.
The flotation allowed the Glazer family to sell 16.7m shares - equal to a 10pc stake.
The Glazers bought the Premier League football club for £790m in 2005 in a controversial deal that enraged fans because they put in just £300m of their own money and loaded the club with debt.
The club's most recent annual results showed total revenues of £320.3m for the year to the end of June 2012, down 3.3pc on a year earlier.