Along with buying a defender, would Cahill be an awful extra signing on a free? I feel like the defence and team in general is lacking a player like him that has experience of successfully playing at the top, model professional, has leadership qualities, good on the ball, a goal threat from corners, someone that is Vocal and a Organizer.
I can remember Fergie doing something similar with bringing Blanc in to the team for his experience and to be honest I would prefer Cahill over most of our current central defenders.