The way I look at it, this game will dictated by how Jose Mourinho sets up his side tactically because we've seen many faces of Manchester United over the last couple of seasons. We've seen them playing really positive, creative football, but on other occasions and - maybe too often for the liking of a lot of people, including their supporters - they've also been very functional at times, very difficult to break down and not very creative.
United are relying on grinding out results rather than going out and playing open football. The system has worked for them to some extent, but I don't think it gets the best out of the players that they've got. You'd like to see them play with a bit more freedom and I think there's a lesson for everyone how City have played. At the start of the season I thought United were more attack-minded but gradually they've come to play with less freedom.
Pressure on United to show they're best of the rest
Given the ferocious battle on for a top four spot, both teams will feel they need to get three points and will want to take risks in order to do so. Particularly Manchester United, who may be second on table, but the gap continues to grow between them and Manchester City and the shadow the leaders cast over everyone beneath them just gets bigger and bigger. After good summer transfer business United were geared up to deliver success this season so to be so far off the pace against City and the gap getting bigger, there's real pressure on them to show that if they can't beat the top of the league, then they can beat teams around them. I think the onus is on them on Sunday.
Midfield trio key to Chelsea's chances of success
I think this one is almost impossible to call. The one thing you can guarantee at Old Trafford is the opportunity as a visiting team to take the game to them. It's a massive pitch, it's a great atmosphere, I always loved playing there myself because you knew if you were confident you could create chances. If Chelsea go out with a positive attitude and an intention to get their creative players on the ball then they can cause United a lot of problems.
N'Golo Kante, Eden Hazard and particularly Willian all played very well against Barcelona during the week and if you can play well against what is one of the best teams in the world, if not the best, then you can certainly do the same against a United team which looks a bit more vulnerable than it used to.
Lukaku and Matic will be motivated
The game can be won and lost in any area of the pitch but ultimately if Chelsea are going to take the game to United then obviously the players they've got to look for are those three. But equally their defence will have to be very solid. United do offer a big threat, and Romelu Lukaku, Juan Mata and Nemanja Matic won't lack for motivation against their old team, so there's a lot of individual scores to settle.
I suppose back stories should motivate players to play well and be the star player, but equally from a defensive point of view, up against the sort of quality of Alexis Sanchez and Paul Pogba (if he plays and plays to his potential) you've got to be really switched on to make sure you don't make a mistake because it could prove very costly.
I thought the key to United's success at the beginning of the season would be whether they could unlock the potential of Pogba and that seems to be the biggest question of them all right now - is he becoming a better player at United than before he signed? That was the main focal point this season for them, but it continues to unravel on a weekly basis at the moment.