Walker is exhausted, he's played pretty much every game, and as the junior member of the defence I don't think he can take much blame for our recent woes. He's had to cover most of the right flank all on his own.
Charlie is a good player, I just feel he isnt good enough in any position and I don't feel he wants to be a utility player.
Not got the pace of a full back, not strong or commanding enough to be a centre backs, and I've not seen enough of him to know if he would be a good defensive midfielder option, but you would need to play 3 central midfielders to make up for Charlie's lack of mobility.
He's a good player, but I prefer Walker at right back and Charlie is too leaden footed to come in to the team without being match sharp, as that performance against PAOK at home showed.