Manchester - Sir Alex Ferguson insists the much-criticised Glazer family have done a good job as owners of Manchester United.

United fans have mounted protests against the Glazers from the moment the Americans bought the Premiership club in 2005, and the discontent has increased significantly over the last 12 months.

The Glazers have amassed debts of over £700 million in the last five years, with United manager Ferguson receiving less money to spend in the transfer market under their ownership.

Supporters at Old Trafford now turn up in green and gold scarves that recall United's colours from the club's early days, in an attempt to deny the Glazers any merchandising profits.

Ferguson, speaking in a CNN interview, is tired of the constant abuse suffered by his employers because he says the Glazers have given him all the financial support he needs.

"The debt has come about by the club being bought out by an owner. You know full well that when a business is bought it is usually bought with debt," he said.

"Because it is a football club it seems to attract more negative reporting from the media and from the fans, but Manchester United football club, when it went public, was always going to be bought.

"It was inevitable. So when a particular family like the Glazers have bought it, it's unfair they come in for criticism, because anybody could have bought it.

"I have to say they have done their job well. They support myself, the manager, and they have supported the players. I have never been refused when I have asked for money for a player.

"So what can I do other than carry on the way we're doing it and the way I'm allowed to carry on. I have no complaints."

As Ferguson prepares to start his 24th season at United, he is aware of speculation that he may retire if his team regain the Premier League title.

United need one more league title to set a new record of 19 English championships and, at 68 years of age, that could be the perfect way for Ferguson to bow out.

However, the Scot is just focused on winning back the title from Chelsea and he emphasised his desire to carry on for as long as possible.

"A lot of factors come into most important things. I'm at the right club. It's a fantastic club, it demands a challenge all the time," he said.

"Every day, every year, there's the challenge of being at the top and that helps me. I think you need good natural energy and I have been blessed with that.

"I'm very fortunate about that, so I'll keep going as long as my health keeps going. The same applies to every person. I'm 68 and so far my health has been standing up.

"If I have my health I can carry on. There will be a point when I do quit but I have absolutely no idea when that is.

"I tried that a few years ago and it was an absolute disaster.

"Agony. My wife made me change my mind and she was dead right.

"I think she was soon fed up with me in the house. Now when the time comes I think the club should be okay."