Centre-back Mills picked up his fifth booking of the season in Saturday`s 1-1 draw at Watford and will serve an automatic one-match ban with Zurab Khizanishvili is likely to take his place.
On-loan midfielder Mikele Leigertwood is expected to make his debut after signing from QPR on Monday on a deal until January.
Defender Ian Harte is fit to face his former club after overcoming a trapped nerve which caused him to be replaced at half-time against the Hornets. Midfielder Jay Tabb also came off last weekend with a dead leg but he has recovered in time to face the Whites.
Club captain Ivar Ingimarsson remains a long-term absentee with a hamstring problem as does central midfielder Brynjar Gunnarsson who continues to struggle with a thigh problem.
Striker Noel Hunt will be hoping to continue his good form following his 15 months out through injury having netted three goals in the Royals last three games.