1) Overload the wings
Let's start with the tactic David Moyes is likely to utilise. After all, this is the team who have attempted more crosses per game (27) than any other side in the Premier League. The mantra seems to be 'get it wide, get it in the box' and this could possibly reap dividends against a Chelsea team who can leave their full-backs exposed. With attacking full-backs and wingers, they could force Chelsea's attacking midfielders out of the central area and widen the pitch to suit United's strengths. At Old Trafford, David Moyes did not have the courage of these convictions as his lop-sided line-up featured Danny Welbeck on one flank and Antonio Valencia on the other; they struggled to create anything at all.
The only time Valencia and Nani have started a game together this season was in the 5-0 thwacking of Bayer Leverkusen, while United have won three of the four games featuring Valencia and Ashley Young. Although the opposition was pretty rotten in comparison with Chelsea, playing both Adnan Januzaj and Valencia against Aston Villa's narrow 4-3-3 resulted in a 3-0 cruise. United cannot afford to allow Chelsea to dictate the shape of the game; overloading the wings could give them the initiative.
2) Play Januzaj as a No. 10
The evidence is hardly compelling as Adnan Januzaj's start as a No. 10 against Swansea ended with him out wide and looking radically more dangerous for the switch, but against Chelsea he is likely to face David Luiz in that central area and David Luiz's capacity to drop a ricket - in this case a rash challenge - could be United's friend on Sunday. There's a reason that Chelsea have bought Nemanja Matic; they recognise that there is a weakness in the centre of their midfield that makes them vulnerable to direct running. They certainly struggled with Ross Barkley at Goodison Park.
The case for Januzaj is also strengthened by the likely absence of Wayne Rooney, with Shinji Kagawa the only other viable alternative. As much as United fans would like to believe otherwise, he simply hasn't done enough in that No. 10 role to justify inclusion against a Chelsea side so far into their stride that the stumbles of November look a million miles away. Kagawa could get lost against Chelsea's two defensive midfielders while Januzaj could at least get clattered.
3) Man-mark Hazard
The first of our suggestions was to impose United's game on Chelsea; this involves a tacit admission that a) Chelsea are much, much better and b) in Eden Hazard, they have a man whose extraordinary form demands special treatment. Mind you, this was something tried by Gus Poyet at Sunderland and here's what he said after Hazard scored twice and made another goal when they met in December: "We tried everything - we man-marked him, we put two up against him, three, tried other tactics but there was nothing we could do." But despite the evidence of their Capital One Cup clash, United are a better side than Sunderland and would presumably do a better job of limiting Hazard.
This tactic would depend greatly on the personnel available as Phil Jones is probably the only United player you would trust with the job (at least with Darren Fletcher only 90% fit). He was entrusted with man-marking Cristiano Ronaldo and Marouane Fellaini by Sir Alex Ferguson with encouraging results. The problem with man-marking Hazard, of course, is that you're leaving space for two of Oscar, Willian, Juan Mata or Andre Schurrle to operate in the middle against just one central midfielder - presumably Michael Carrick. Would Moyes take that chance?
4) Play three at the back
Clearly this is is unlikely to happen - United are managed by David Moyes, not Brendan Rodgers - but this was a tactic that caused Roberto Di Matteo's Chelsea all sorts of problems last season when deployed by Liverpool, Manchester City and, most notably, Juventus (mind you, Di Matteo walked straight into Juve's grateful hands by playing Hazard as a false 9. It did not go well.). But this is Jose Mourinho's Chelsea and they're nowhere near as vulnerable as their previous incarnation.
Moyes does have form for this formation - he tried it towards the end of last season in an attempt to get the best out of Leighton Baines and Seamus Coleman - and there is a pretty compelling argument for using Patrice Evra and Luis Valencia in those wide positions to stretch the game (particularly if Nani and Young are still unavailable), while giving United an extra body in the middle to deal with runners from midfield. The system has its flaws (expecially against a Chelsea side who need no invitation to attack through the middle) but its biggest plus point for Moyes on Sunday could be the element of surprise. It will take Chelsea 15 minutes to adjust and United might already be 1-0 up and preparing to sit back with a five-man defence (plus Carrick and Fletcher).
5) Pay the referee
Because in the laws of journalism you can never have Four Ways Something Can Happen.