So, let's see. You want to get rid of a player like Fernandinho who will still play an important role next season. At his age and salary we wouldn't get much for him and would almost end up giving away a 30M quality player, we'd also keep an injury prone player and try to buy a player that maybe isn't even for sale for much less than Walker for all we know.
The alternative is to spend a few million extra on Walker and keep Fernandinho. I know which I'd go for and which makes the most business sense.