3) Diego Costa injury a big blow
Chelsea have done best against Arsenal with Didier Drogba at his peak playing upfront against the Gunners. Although the Ivorian is likely to start at the Emirates Stadium this weekend, he is no longer at his best and looked poor in the games against QPR and United. Diego Costa’s injury is a big miss for Mourinho as he is exactly the kind of player Arsenal struggle to cope with, and his excellent goalscoring form this season has seen them through some difficult games.