"The Board notes recent press speculation regarding a possible bid for Manchester United," said a statement.
"The owners remain fully committed to their long-term ownership of the club. Manchester United is not for sale and the owners will not entertain any offers."
The club's American owners, the Glazer family, have been under pressure to bow to a group of wealthy supporters, known as the Red Knights, who want to buy the club.
Fans of United, league runners-up and Champions League quarter-finalists last season, have launched a 'green and gold' campaign to oust the Glazers after critics said they had saddled the club with too much debt.
Friday's statement came with the Old Trafford club's quarterly financial results which announced a cut in debt from 543.3 million pounds a year ago to 520.9 million for the January to March period.
The club showed net assets of 794.9 million pounds and a cash balance of 95.9 million. In the nine months to March, year-on-year revenues were up 14 percent from 193.3 million pounds to 219.3 million.
