In this fixture last season, Chelsea handed Manchester United and their former manager Jose Mourinho a 4-0 humiliation. But, even though the Blues are the Premier League's reigning champions, the roles feel somewhat reversed ahead of Sunday's 4.30pm kickoff at Stamford Bridge.

Chelsea enter the weekend in worrying form and amid rumours of discontent following a 3-0 drubbing at the hands of Roma in midweek, while United have failed to win just twice in the top flight so far this season and have their sights firmly set on clinching the title.

In order for Antonio Conte to ensure his side bounce back from recent events to claim a win over the Red Devils, he must find the right answers to these three crucial questions.

Who starts in defence?

For all the talk of disruptions behind the scenes affecting Chelsea's form, their biggest problem is obvious - a defence that has conceded 13 goals during the last seven games. And in turn, the underlying factor behind that has been the constant changing of personnel, partly due to the Blues' Champions League commitments and partly due to a series of injury problems.

The good news is that Antonio Conte has all of his centre-back options available to him for Sunday, but the resulting dilemma is who should actually start. Reverting to last season's back three is the logical and probably most sensible option, but captain Gary Cahill hasn't exactly convinced this term and Cesar Azpilicueta may be needed at right wing-back ahead of Davide Zappacosta.

This is easily the biggest selection decision Conte faces ahead of Sunday's game - United's whole game-plan centres around capitalising on mistakes at the back.

Can Bakayoko and Fabregas cope in midfield?

For all the criticism of Chelsea's performances at the back, they certainly haven't been helped by Cesc Fabregas and Tiemoue Bakayoko in midfield. Neither are defensive-minded players; the former is a playmaker and the latter is, at his most defensive, an industrious box-to-box; and for differing reasons, both have looked exceptionally leggy in recent outings.

Considering how crucial the midfield battle will likely be on Sunday, sticking with the current formula and hoping for the best seems like a huge risk on Conte's part. He'll of course be hoping N'Golo Kante recovers in time to make the starting XI and that could transform the whole team when out of possession, but the Frenchman remains a doubt.

The obvious alternative is to change the formation and bring an extra body into midfield in the form of Danny Drinkwater. That will at least ease the burden on Bakayoko and Fabregas' legs, and add an extra layer of protection in front of the defence.

How can Chelsea penetrate Man United's defence?

A question only two Premier League teams have found the answer to - how to actually get past United's defence. The Red Devils have claimed eight clean sheets in the Premier League already this season, only conceding to Huddersfield and Stoke City, including against Liverpool and Tottenham.

To make matters worse, Mourinho is almost certain to set up his side as defensively as possible on Sunday, making it even harder for them to break through. United are so physical and well-organised in defence it's hard to identify a weakness.

But Chelsea do have one of the deadliest creators in the Premier League to fall back on in Eden Hazard and if there's one potential failing the home side can exploit, it's United's lack of familiarity with 3-5-2 - the formation Mourinho looks set to utilise once again after matching up with Tottenham last weekend.

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