Manchester United's share price rallied after dipping during the day as Sir Alex Ferguson confirmed his retirement.

From an opening price of 18.77 US dollars, the shares fell by as much as 4.5 per cent to under the 18-dollar mark and then revived significantly.

The value of a share at the close of trading was 18.44 dollars, 33 cents down - a 1.76 per cent drop - and still higher than the share price on Friday last week.

"We are highly dependent on members of our management, coaching staff and our players," United said in its IPO prospectus.

"Any successor to our current manager may not be as successful as our current manager."