I'm assuming his thinking must be that Henderson is the closet thing we have to a DM with lucas out (Gerrard, Sahin and Shelvey are all better attacking) and he wants someone with good stamina sitting in front of the defence to try and keep Michu quiet.
Then he wants Enrique on the left wing, but with Wisdoms taking a knock on Thursday, means that Johnson has to play at right back, so the only alternatives to play at LB are Downing and Robinson (and guessing he isn't ready to trust Robinson just yet)