Even though I'd much rather see him on the left, meaning Nani on the right to continue his good relationship with Rafael this season... Well either wing there's potential good combinations
For a start :
Costa plays on the left. Evra is great with overlaps, Anderson and Costa speaking the same language might mean Anderson combines well with him when playing left central midfield
Costa plays on the left with Fabio at left back and Anderson left central midfield. 3 Brazilians, 2 left feet and 1 right footer who likes to get forward and have a shot.
Costa plays on the right with Rafael bombing forward into the space a left footer leaves. Again, same language and could perhaps see the best of Rafael attacking
Costa certainly wouldnt be a player I'd have suggested, but we could do a lot, lot worse and he's clearly a talent who would likely fit in with the other players we have. And we've been interested in him before.