He has been in & out of my team over the past 24hrs, I've decided against it as I'm not taking on any players who haven't had a clear preseason.
It has been 3 weeks since he had that niggle, note I say 'niggle' as I read that it wasn't iced when he came off or after the intra game, maybe he felt something and didn't want to risk it...? As far as I can tell, he's been back in full training for the past week and he looks the fittest I've seen from training photos posted. I feel that if there were any doubts, they wouldn't risk playing him as he's probably one of the most important piece of our puzzle. A lot of our forward foray stems from his run and carry and ability to pin point a pass.
The element of injury risk applies to all players, some more than others. One needs to also factor in their role as well when they are assessing this risk. The flipside is that Hall has shown last season that he has all the tools to be the top defender and our game style out of defense is centered around him. I see him as a classic 'risk v reward' type selection, different this season is you're forking out a premium for him compared to last season.
In summary, my suggestion to you (and others considering him) is that if you feel confident that he'll enjoy a significant gap (say 5+ points) to the other defenders then the risk is worth taking on.
Good luck on your decision, I'll enjoy watching him regardless of whether he's playing for my team or not.