McDaniels, Toub, or Wilks.
Apparently Wilks and Ballard were in Chicago together from 06-08 when Wilks was the DB coach and Ballard was a scout. Ballard's coaching background is as a WR and DB coach so it's likely their paths crossed.
According to SI (
https://www.si.com/nfl/2017/12/14/st...nthers-defense) Wilks is likely to bring Carolina DL coach Eric Washington with him to be DC.