For me be prepared is hard unless I know player is going out. I think that it's cause I try to adapt tactics to the team strenghts not trying to buy players and making them fit into mine tactic.
Right now I'm playing with Middlesborough(FM Whizzkidz database) I'm 9th and I'm into first season x-mas. So I did know their team is good for sitting deep and playing counter attacking football. So I made my tactic for that well all three tactics are counter attacking tactic but different formation thanks to flexibility into team.
At this time into season just about 10 days for january transfer window I know I'm going to need new AM cause Ramirez wants leave plus new DLP (thanks to injury of De Roon) who can defend and still run the game into deep(Watch Xabi Alonso, Pirlo) but still I don't know who I want to buy or who are available for me.
I did buy Ivan Ordets from Donetsk already cause I know Chambers is going back to Arsenal after end of season but for honesty I would not have bought him unless his agent wouldn't come to me.
So how you keep yourself prepared for situtations that someone leaves? Yes I scout but only in regions not into specific positions. And some kind shortlist but at the moment there is only youngsters or players who aren't really available to Boro.