It's so he can accomodate his CMs and go back to the formation that he knows best. It'll probably be something like: Cech, Cole, Gallas/Carvalho, Terry, Ferreira, Makelele, Essien, Ballack, Lampard, Drogba, Shevchenko With Essien making way for Cole/Robben (most likely the latter) every now and then, and Lampard playing in Essien's position.