The City striker was expected to be back in contention after his fitness programme against Arsenal on October 27.
But Fowler will now be amongst the substitutes on Saturday, along with Steve McManaman, who is returning from an Achilles problem injury.
"Robbie spoke to me and said he wanted to come back he knows I am short of a few players. It is his decision and I know it is right,” the City boss told the official club website.
"I have talked to him. He is right and he really wants to be a part of it. I have never ever lost faith in Robbie Fowler.
"He is fit and strong. He will need a goal and the confidence will flood back for him."
Keegan has also added reserves defender Nedum Onuoha to the squad. The 17-year-old played in the pre-season friendly against Bury and may join two other former Academy players, Stephen Jordan and Willo Flood, on the bench.