Manchester United's Champions League place won't be secured by their position in the Premier League table—as a top-four finish is just out of reach. United's future will be decided by how they fare in this season's UCL competition.
Should United win the trophy, they'll secure a place. If they're knocked out, so are their European hopes for next season.
The Red Devils won't be expected to win against Manuel Pellegrini's side, so other than pride, Manchester United have nothing to lose.
Manchester City—on the other hand—have everything to play for. Their three games in hand over league-leaders Chelsea will be reduced to two after Tuesday, so to keep pace with the London side, City need points.
In their 5-0 demolition of Fulham, the Citizens employed a 4-2-3-1 formation. With their captain Vincent Kompany out due to a red-card suspension, Joleon Lescott was brought into the side along Martin Demichelis.
The Cottagers going down to 10 men helped City without question, but keeping a clean sheet under any circumstance gives any defence quiet confidence. With their Belgian captain reinstated, you'd expect Pellegrini to continue his centre-back partnership of Kompany and Demichelis against United.
City have enough quality in midfield for two Premier League sides. The double pivot of Yaya Toure and Fernandinho scored four of the Sky Blues five goals last Saturday and should be automatic selections at Old Trafford.
Joy can be found on the wings against United. David Silva and Samir Nasri would be expert selections, combining with their accompanying full-backs and bombarding the United penalty area.
As the Red Devils' centre-back partnerships have been less than serviceable this season, Pellegrini would be well served to play with two strikers up top. Sergio Aguero will not be available for Tuesday's fixture, according to BBC Sport, so the pairing of Edin Dzeko and Alvaro Negredo should be enough to keep United's defenders occupied.
For this aim, the 4-2-2-2 formation would suit the Citizens perfectly.
Now to the home side.
United boss David Moyes has been much maligned in recent weeks for (seemingly) not having a plan. Let's try to give him a blueprint.
With Chris Smalling out for a month, per Mirror's Alan Nixon, the weekend-rested Rio Ferdinand should get the start if he's fit; likewise, Patrice Evra should claim his left-back position from Alexander Buttner.
United should be attack-minded. There's no upside to playing tight, as City have proven they'll eventually break any side down—no matter how big the parked bus; as the old adage says, sometimes "your best defence is offence."
Playing three central midfielders would give Moyes a fighting chance to retain possession or—at the very least—offer his team spells of relief.
Ryan Giggs played expertly in United's 3-0 Champions League comeback over Olympiakos last week, showing his quality by finding willing runners and outlets. Michael Carrick has a similar game and is the best central-midfield option at Moyes' disposal.
As an anchor man, Marouane Fellaini represents the Scots' optimal choice. He's physical, imposing and can find a pass. This is contingent on the Belgian avoiding a ban, as noted by the Express' Matthew Dunn.
The Dutchman's exit from the side allows Wayne Rooney to play as a striker and Juan Mata to play in his preferred "No. 10" position. If Moyes wants to give City's suspect centre-back pair issues, he should add Shinji Kagawa to the mix, not on the wing, but in the middle of the park with Mata.
The 4-3-2-1 formation, also known as the "Christmas tree," would fit this goal entirely: Rooney, Mata and Kagawa as United's attacking trident, with Giggs, Carrick and Fellaini providing cover and quality linked play.
Who will win the Manchester Derby?
Should Moyes' squad be a measure leaky, the change to a 4-2-3-1 is simple. With Fellaini and Carrick in the double pivot, Giggs on the left flank and Kagawa on the right.
The game should be an interesting spectacle; tension at Old Trafford will be palpable, as United supporters won't want another hiding on their hands. Nevertheless, the world's richest derby is sure to impress, sure to frustrate and is sure to be an important factor in determining the Premier League crown.