Fergie's fight to find the next generation

But by United's high standards last season was only just acceptable - a 3-0 win over Millwall in the FA Cup Final partly redeeming a third-place finish in the Premiership, a Champions League exit to Porto and a Carling Cup defeat to West Brom in the fourth round.

And this season? Well, the title already looks a lost cause, raising the prospect of United's name absent from the trophy in consecutive seasons for the first time since the Premiership began in 1992-93.

Non-League Exeter stand between United and their defence of the FA Cup while AC Milan eagerly await their Champions League date with United next month.

First, though, Ferguson must once again outwit Jose Mourinho. In Mourinho's firstever Premiership match, Chelsea beat United 1-0 at Stamford Bridge in August.

Tonight United visit Chelsea for the first leg of the Carling Cup semi-final. After Saturday's humiliating experience against Exeter, Ferguson can't afford to entrust this job to his boys.

The trouble is, some of his big-name players need a rest after an exhausting programme of games over the holiday period. That's why he fielded so many second-string players against Exeter. But for Ferguson, it's impossible to avoid the conclusion that time is finally catching up with the best team of his era.

Giggs is now 31. Scholes is 30, Gary Neville is 30 next month and Phil Neville is 27. Butt and Beckham have both left the club. Roy Keane, an inspirational figure for nearly 12 years, is 33. Had Ferguson retired two years ago, as he planned to, the job of replacing these players would have fallen to a new manager. Ferguson could have left with his magnificent legacy intact.

By changing his mind and deciding to stay, he accepted the challenge of rebuilding his team - and this has proved far more difficult than he anticipated.

For instance, balanced against the capture of Ruud van Nistelrooy, Rio Ferdinand, Wayne Rooney and Cristiano Ronaldo are the less convincing signings of players such as Juan Veron, Kleberson, Eric Djemba-Djemba, Diego Forlan and a clutch of indifferent goalkeepers.

This rebuilding process reminds us of the treasures Ferguson unearthed in his youth ranks more than 10 years ago. With Beckham, Butt, Scholes and the rest came an inbuilt team spirit, a sense of purpose and a love of the club.

Even with a Roman Abramovich-size cheque book there is no guarantee that these qualities come as standard when you dip into the modern transfer market. Ronaldo may have a wonderful touch and a bagful of tricks but if it's a winning mentality you want you'd choose Beckham, wouldn't you?

Ferguson has taken much for granted at Old Trafford over the last decade - and who would blame him? But times are changing. Arsenal, and now Chelsea, have brought a new urgency to United's agenda.

In the short term, this is an important week for Ferguson with a visit to Liverpool and an FA Cup replay at Exeter following tonight's clash. He will not want to finish another season empty-handed.

In the longer term, he's a proud man who wants his successor to inherit a buoyant legacy that will serve United well for the next 10 years.

That is the last great challenge for British football's most successful manager.