Mikel Arteta has been one of the most important players for Arsenal this season. He has operated as the deepest-lying midfielder, linking the play between defence and attack. He has played 33 out of Arsenal's 37 Premier League matches, playing 2956 minutes (second highest, after Santi Cazorla, out of all Arsenal players). He played 90 minutes in every game that he has started except against Spurs (he was technically substituted after 90 minutes against Wigan).
It is disappointing that the Spaniard is injured for one of the most important games of the season. Wenger will most likely deploy a three man midfield as he has started with a 4-3-3 in almost every game. He could play two deeper midfielders and one attacking midfielder or one defensive midflieder (most likely is Ramsey) and two more-attacking midfielders. Wenger has a few options, each one with their own positives and negatives.
One of the more obvious options is playing Jack Wilshere and Aaron Ramsey as the two defensive midfielders. Both are hard-working and they have played together this season, but Wilshere has not had much game time recently and he sometimes gives away unnecessary free-kicks. Wilshere could also play as one of two more attacking midfielders. Wenger said concerning Wilshere, "He is an option, yes. We will monitor him until Sunday and I will make a decision
very late over what I will do."
Rosicky could drop into Arteta's position alongside Ramsey, which would allow Cazorla to play as the central attacking midfielder. Rosicky has similar pros to Jack Wilshere but sometimes gives the ball away irresponsibly, which is not an ideal quality for a man protecting the back four. Rosicky and Cazorla could play as the pair of more atacking midfielders.
Francis Coquelin is one of the few players who has some experience playing in this position. The only disadvantage is that he hasn't had many minutes on the field recently and sometimes not even making the bench.
Thomas Vermaelen is not a name that would automatically spring to mind, but I think he would be a good option. The club captain has struggled for form and hasn't had much game time, but his attributes suit the position well. He reads the game well and knows how to defend. A big complaint from some Arsenal fans is that he dives into tackles, those tackles are more suited for a defensive midfielder to break up the play. His distribution is not great, but he would occasionally offer another strong physical presence in the box with the other defensive midfielder covering the back.
Thomas Eisfeld is a more attacking player by trade but has played a more defensive role on a few occasions. His most impressive performance for Arsenal fans was in the cup win over Reading, linking up the play nicely. He lacks experience (which is crucial for a game with such high stakes) and an understanding with the rest of the players.
Thankfully Wenger, and not I, has the tough task of choosing Arteta's replacement. All of the candidates are good options, but I think the most likely is Jack Wilshere. As always there will be fans and "pundits" that like the decision and those that don't.