Mike McGraw hints at it here:
Bulls guard Kyle Korver said Monday he's been bothered by a cyst in his
left ankle. He had a cortisone shot, but is hoping surgery will not be
CSN's video update discusses it more saying that if his condition doesn't improve he'll require surgery. Also on the update and linked elsewhere is that Keith Bogans may miss tonight's game with a sore back.
For his part, Korver's said the injury is getting better after the cortisone shot, but it isn't fully there yet. I'm not a doctor, and I don't know how cortisone would be used to treat this condition specifically, but in my experience with people getting cortisone shots is that if the condition doesn't improve more or less right away, it typically isn't going to get any more benefit from the cortisone.
In that case, I'm concerned that this is going to be an issue which eventually requires surgery, but we'll have to wait and see.
As for Bogans, his issue seems unlikely to effect him going forward.