The former Reading and Leicester City man is facing a spell on the sidelines after suffering the injury in the course of his defensive duties at the weekend.
The injury has yet to be officially announced by Bolton Wanderers but it is understood that Mills is facing a break of some weeks, leaving manager Dougie Freedman short at the back.
The likelihood is of course that Zat Knight will be drafted back in alongside David Wheater, meaning no respite for the former Middlesbrough man who has just returned from a serious knee injury himself. Fellow centre half Tim Ream is covering at left-back following the broken ankle suffered by Marc Tierney.
Wanderers also recently recalled centre half Cian Bolger from a loan spell at Southend after the Irishman suffered a knee injury on his debut this past weekend.