Shares closed at 110p after the new signing was announced and were trading at 107p at 11.30 GMT today.
With the England central defender's wages set at about £3.5m ($5.5m) per year, the deal is expected to cost the club £10m ($15.6m) each year of the five-year contract.
If Ferdinand had not been bought, analysts calculate that shareholders could have benefited from a 170 percent increase in dividend payments.
According to Collins Stewart analyst Stephen Ford, quoted in the Financial Times newspaper: "Manchester United shareholders, who have seen the share price fall over the last couple of years, may have preferred to see less money risked in player trading and more returned through the certainty of dividends."
The club has said that players will be sold to help finance the Ferdinand deal, but the obvious candidates for sale, such as Juan-Sebastian Veron and Dwight Yorke have failed to attract suitable buyers.
Separately, Manchester United today announced that razor maunfacturer, Wilkinson Sword, had signed a four-year sponsorship and licensing deal with the club, becoming United's first-ever 'grooming partner'.
No figures were given on the deal, which was not sizeable enough to warrant a stock exchange notice.
Shares in English Premier League giant Manchester United fell by 8.5 percent yesterday, following the club's decision to buy Rio Ferdinand for £30million ($46.94m/EUR47.4m).
