The central defender has been missing since the opening day of the season due to an ankle injury but should be back in training towards the end of the week and put himself into contention to face Billy Davies's side.
A target for the Reds during his Doncaster days, Mills told the Reading Post: “There was a chance of potentially going to Forest, but I don’t think the chairman at Doncaster was prepared to let me go to what they considered a rival club at the time.
“To be fair whatever they offered was annulled by the chairman not wanting to let me go there.
“So it was a bit of a strange situation. But it’s Reading’s gain I guess. I’ve had a great last six months since I’ve been here and an amazing pre-season."
The two sides played out a goalless draw at the Madejski Stadium on the opening day of last season.