Personally i wouldn't even take Glen Johnson.
For me he looks a liability defensively and even if Carragher doesn't get forward as much,we'd already have Ashley Cole(probably) going forward and Bridge if he plays.Gary Neville can put a good cross in but hasn't had his best season from a defensive point of view,but Johnson would be one for the future.
Looking at the attacking talent in the midfield i don't think we desperately need an attacking full back,it's just that on the left the best and most likely to be picked offer that option.