Mills, a former City loanee is back from suspension and is likely to go into the team along with Jimmy Kebe, who scored for the Royals in the 3-0 win over the Sky Blues in the corresponding fixture last season.
Coventry City are likely to be unchanged from the team that beat Middlesbrough with manager Aidy Boothroyd reporting no new injury problems.
Aron Gunnarsson is expected to make his 100th appearance for City.