Manchester United shares sank four percent in opening US trade Wednesday after the football club’s legendary manager Alex Ferguson announced his retirement.

In the early minutes of trade, the shares, listed on the US Nasdaq exchange by the club’s US owners last year, were off 4.1 percent to $18.01.

Earlier Wednesday, the Premier League champions shocked the sporting world when they announced that Ferguson will retire at the end of the season, ending the most successful managerial reign in English football.

Ferguson, 71, guided United to 13 Premier League titles and two European Champions League crowns in 26 years in charge at Old Trafford.

He will remain at United as a director and club ambassador, and said he was confident he was stepping down with the team in good shape.

“The decision to retire is one that I have thought a great deal about and one that I have not taken lightly. It is the right time,” Ferguson said in a statement.

United, owned by the family of US investor Malcolm Glazer, did not immediately name a replacement, but most speculation focused on Everton’s David Moyes to fill Ferguson’s seat.

Despite the fall at the news, the team’s shares were still trading 27 percent above the $14.00 initial public offering price last August.

At that time the shares barely treaded water amid worries over the team’s ability to dig out from under a pile of debt.

But they rebounded beginning in November with improved quarterly profits thanks to a slew of sponsorship deals and huge tax credits and a reduction of their debt burden, acquired in 2005 after the Miami-based Glazers’ heavily leveraged takeover.