Loose cannon: United winger Luis Nani has been on form

In the early hours of 23 May 2008, drenched in both the Moscow rain and the sensation of glory, Alex Ferguson was rhapsodising about European dynasties. His Manchester United squad may have just beaten Chelsea to the Champions League trophy with a slice of fortune, but he was confident they also had the depth to go on and claim the succession of victories he long desired. "I think you can call this a great team... and we can get better with the young players coming through."

Ferguson was right on the first point. Indeed, not only could he call his side great, but arguably United's greatest. That night in the Luzhniki Stadium was the high point of a three-season spell in which they won three straight domestic titles, the Carling Cup and that Champions League. Since they also reached another European final the following year, it was the most concentrated period of success in the club's history.

What's more, it was unique in Ferguson's entire career in that his team were at the forefront of tactical advances in the game. Unlike an innovator such as Jose Mourinho, the United manager had always adapted to trends. Yet, with the heavy involvement of Carlos Queiroz, he pioneered a strikerless 4-3-3-0. It was built on an airtight defence and topped off with a thrillingly fluid attack of Wayne Rooney, Carlos Tevez and Cristiano Ronaldo. Only strengthening the feeling that this was the team of the future, the average age of that trio was 23.

Except for the fact Ferguson was wrong on the second point. United haven't got better. In fact, they've got a good deal worse. Possibly their worst since 1992. Unlike in 1999, Ferguson had no injuries or suspensions to work around for that final against Chelsea. So the team he sent out was his first-choice. It's remarkable how quickly it's broken up or diminished.

Edwin van der Sar is on the verge of retirement and allowing errors to slip into his game that were inconceivable in 2008. Ahead of him, both Wes Brown and Rio Ferdinand have been ravaged by injuries. Nemanja Vidic and Patrice Evra are, admittedly, at the presumed peak of their careers. But Vidic's aura has evaporated somewhat since repeated eviscerations at the feet of Fernando Torres while Evra has suffered a post-World Cup slump.

In the centre, United's midfield then took charge of games rather than chugging through them. Owen Hargreaves's energy gave Michael Carrick the space he requires to pick passes while freeing Paul Scholes. With Ferguson now publicly doubting whether Hargreaves can ever be the same, Carrick has encountered more pressure in midfield and his confidence has dissolved. Only Darren Fletcher can mimic Hargreaves's motor but he can't sustain it for more than a match a week.

Up front, United had one of the European Cup's great forward lines. The stats emphasise that. But Ronaldo and Tevez have now gone. And, for the last seven months, Rooney may as well have been.

What's left is a squad that appears patched together, between eras. In perhaps the greatest contrast to 2008, United suddenly seem devoid of dependable match-winners. Rooney has been absent and in recovery, Dimitar Berbatov frustratingly erratic. The Bulgarian went from five goals against Blackburn to the same number of missed chances against Valencia. Like much of their squad, Javier Hernandez is still too young while the likes of Scholes get too old. Only Nani has been consistent, emerging as one of the most productive players in the Premier League.

On a whole, United compare unfavourably with Arsenal, Chelsea and even Tottenham and Manchester City in terms of mature match-winners. Arsene Wenger's side, in particular, possess Cesc Fabregas, Robin van Persie, Andrey Arshavin, Theo Walcott and – above all recently – Samir Nasri.

Yet, in spite of that, United's worst squad in 18 years look likeliest to capture that landmark 19th league. Because, instead of relentless match-winners, United still possess the most relentless title-winners.

That night in Moscow, Ferguson also said "you never know what ambition can do". As long as United have their manager's, they can overcome an awful lot. His drive has given them a core consistency absent in each of their rivals. Tottenham, for one, have yet to adapt to the dual pressures of a Champions League campaign and a sudden expectation to deliver. Chelsea are imploding at present. City, meanwhile, seem permanently engaged in a race against time to build a cohesive unit before imploding.

And as exciting as tomorrow's opponents are, Arsenal are still much less than Barca light. They're effectively half the Spanish champions: similar to Barca with the ball; utterly dissimilar without it. Wenger's team don't apply the pressure that makes Pep Guardiola's so devastating.

The manner in which both Rooney and Anderson did so on Tuesday, however, shows they're both recovering something like optimum form. United are nowhere near theirs or the sort of performance that cut Wenger's side apart in January, but they're unbeaten thanks to the fact different players have stepped up when required. None consistent, but all just about coming together. Recent form, then, suggests tomorrow's tie will come down to whether Arsenal's dazzle can overcome United's doggedness. Because, for the moment, this United may not be great. But they possess a lot of grit.