Mills, who joined Reading from Donaster, was sent off during Reading's game against Ipswich Town on Saturday for a challenge on David Norris.
Reading announced this lunchtime that they are appealing against the dismissal and under normal circumstances, the appeal would have been heard before the next fixture but with the game against the Sky Blues tomorrow, Mills is eligible to play pending the appeal.
Former Sky Blue Jay Tabb could also feature in the game.
Coventry City boss Chris Coleman could make changes from the side which lost at home to Derby yesterday. Freddy Eastwood is still out with a back injury.