Manchester United co-owner Edward Glazer has put three million shares in the club up for sale, expected to fetch about £29m on the New York Stock Exchange.
When former owner Malcolm Glazer, Edward's father, died in May, his shares in the club were spread between his six children.
Manchester United confirmed that the club would not receive any of the proceeds from the sale.
The club holds £362.2m of debt, according to its latest statement - a hangover from Malcolm Glazer's takeover of the club, where he used a series of loans to finance a buyout in 2005.
The share offering is expected to close on 12 December.
On the pitch, Manchester United's season has picked up in the last few games under Louis van Gaal's stewardship.
The Dutchman had endured a turbulent start to his Old Trafford career, but the team has now won five league games on the bounce, to put the club in third position in the Premier League behind cross-town rivals Manchester City and Chelsea, who sit top.