The confirmation that David Silva is out of the Arsenal game, and possibly a couple more, is extremely bad news for City. Kompany has been a rock at the back all year and Nigel de Jong may be the single most important player that City have. But it is the Spaniard who is City's best player and the team will greatly miss the work rate and vision that Silva brings to the table.
The issue will be one of tactics. There appear to be three formations open to Mancini, 4-2-3-1, 4-3-2-1 or the Inter Diamond.
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The most likely of these given the players available is the Christmas Tree 4-3-2-1 with Milner and Johnson playing the 2 and Tevez as a lone striker up front. It's not the most exciting formation and would play more like a 4-5-1 when Arsenal have the ball attempting to clog the midfield.
Normally the 4-2-3-1 is the perfect counter attacking formation and against an Arsenal side used to going forward this would be the preference if City had a fully fit side. How City could use Bellamy and his speed right now; indeed there's an argument to be made that a recalled Bellamy could be the one player that allows City to make a legitimate challenge for the title. But for now, we'll presume that isn't on the cards. In a 4-2-3-1 there are a number of choices. Again Milner and Johnson could play on the wings and Yaya Toure could move forward into the pivotal Attacking Midfield (AMC) role.
An alternative would be to play Milner on the left, SWP on the right and use Johnson as the AMC. A really adventurous option would be a version of the 4-2-3-1 that City played at the end of last year. Then Bellamy and Johnson played on the wings, Tevez ended up playing the AMC role and Adebayor was the striker up top. If Adebayor is available, and I've seen no current injury reports on the Togolese forward, then substitute Milner for Bellamy in that line up and see if the club can replicate the Chelsea result of last year. Even the use of Jo instead of Adebayor in such a scenario would be an interesting wrinkle.
Lastly City could play the Inter style diamond with 2 players up front. Here you would see Johnson play as the AMC with Tevez and Adebayor/Jo up front.
If City come out in a 4-3-2-1 then a draw is on the cards. A 4-2-3-1 would indicate an attempt to snatch a win on the counter attack. Given the way the club played tactically against United earlier in the year, I'm expecting the Christmas Tree and for City to be pleased if they come away from the Emirates with a draw.