The night before Tottenham's defeat to Everton on 5 January, Harry Redknapp dropped his squad off at a Liverpool hotel and got back on the M62 to embark upon a spying mission at Old Trafford. Alex Ferguson's side were hosting Stoke City and the 63-year-old was keen to make a few notes in preparation for today's fixture at White Hart Lane. Redknapp, though, would have been fully aware of the futility of the exercise he was embarking upon. While it's unlikely that casting an eye over Manchester United that evening has harmed Tottenham's preparations for today's game, Redknapp would have known full well that any attempt to figure out from that Stoke game how, tactically, Ferguson might set out his side this afternoon, or indeed what personnel he might use, was a pointless exercise.

Ferguson's line-ups, you see, are about as predictable as the lottery numbers; the formation the Scot chooses on a weekly basis is similarly capricious. The mystery as to why United sit top of the table without having played that well, and why they are where they are despite possessing a squad whose overall quality is far below the mean of Ferguson's reign, could just have an answer in the sleight of hand the manager uses in shuffling his deck.

Take the evidence that's before Redknapp heading into today's fixture as an example. Against Stoke, as the Tottenham manager studiously watched on, United started with what seemed to be a 4-4-2 formation, with Dimitar Berbatov and Javier Hernandez paired up-front. As the game progressed, however, United's formation appeared to be closer to 4-3-3, with Nani playing as a right-sided striker and Giggs tucking into to play as a third central midfielder. The visit of Arsenal before Christmas, meanwhile, saw Ferguson select Rooney up-front in a 4-5-1 formation. The FA Cup game against Liverpool last weekend saw United use a different shape, a 4-4-2 formation that didn't morph into anything else. That's three different formations in three weeks, at a time when the other sides in the title race, or in the top five at least, have been sticking rather rigidly to their own particular default.

Arsenal, for starters, may well change personnel on a regular basis but they stick to Arsene Wenger's own take on the 4-3-3 system with religious fervour. They don't budge from it. Roberto Mancini is similarly rigid in his formation at Manchester City. It, too, is more or less a 4-3-3, with one central midfielder – usually, and confusingly, Yaya Toure – given licence to roam forward from time to time. Tottenham, as we'll see today, are similarly married to one system. The arrival, and success, of Rafael van der Vaart has meant that Redknapp has sent his side out in a 4-4-1-1 formation for the best part of the season, but it essentially remains 4-4-2 with a twist. They can't play any other way. Chelsea, a side who arguably need to change their formation more than any of the others, have also stuck to the same formation. Carlo Ancelotti, a disciple of the Christmas tree at Milan, seems intent on changing his side's fortunes by selecting more or less the same players in the same 4-3-3 formation.

The consequence of all this is straight-forward. When teams sit down to analyse their opponents, they are immeasurably easier to figure out if they play just one way. Look at Chelsea. Sunderland, Aston Villa and Wolves, to offer but three examples, appear to figure out that by playing two men up-front and putting pressure on Chelsea's centre-halves and holding midfielder in possession, the service to the rest of the side is disproportionately affected. In the case of Arsenal, opponents appear to have figured out that by crowding the centre of the pitch and offering them the outside, Wenger's side struggle. An entirely unpredictable United, on the other hand, have remained unbeaten, as their adversaries have struggled to work out where exactly to place the shackles.

Ferguson's player rotation policy causes similar problems for opponents. How is Benoit Assou-Ekotto today, for example, supposed to prepare to face Nani when the Portuguese could easily be asked to play on the left flank, behind the front two or even on the bench? That is one benefit of the rotation system; the other concerns the freshness and hunger of United's squad. The United manager, in 31 matches so far this term, has yet to name an unchanged side. It's nothing new. In 2008-09, Ferguson went the entire 66 game season without sending out the same starting line-up in successive fixtures. "Rotation is a part of the modern game," United's manager has explained. "It's got to be. Look at how fast the Premier League is and the intensity of the matches. The speed of the game has changed and somewhere along the line I have to make changes."

An examination of the Premier League starts made by Ferguson's players this season is a study in the art of squad management. Only nine players have managed 10 or more starts, while 18 have started between one and nine fixtures. Compare this to Chelsea where 13 players have started 10 or more games and just five have started between one and nine games and you realise how good Ferguson is at sharing the load. And how successful it is.

Back to today, and if Redknapp is looking for a pointer for this afternoon he might well look back to Tottenham's visit to Old Trafford in October. Then, Ferguson sent out his side in a 4-4-2 formation, albeit one that was closer to 4-2-3-1 as they attempted to crowd the midfield and cut off the supply to Tottenham's wide men. Who knows, they might replicate those tactics today. Or they might not. With Ferguson, it has become impossible to tell.

FA Premier League: Tottenham Hotspur v Manchester United, White Hart Lane, 4.10, Live, Sky Sports 1, 4.00