Demichelis (knee) has yet to play for City since he joined from Malaga in the off-season, while Rodwell (hamstring) has appeared for just 90 minutes in his club's trip to Stoke.
But both players believe they can play a part in City's match away to West Ham on Saturday after taking on Rochdale in their club's elite development squad.
"It was difficult at the beginning (at City) with the injury but that allowed me to meet everybody at the club and feel confident and comfortable with everybody," the Argentine defender said.
"So it's fantastic now and I'm looking forward to my debut."
"I'm fit. I proved it tonight, played 90 minutes so we'll just wait and see," Rodwell said.
"I've not trained too much, that's why I played tonight.
"I'm fit so I'm available for selection."
"I've played in this position many times before and the manager knew that," Pellegrini said.
"Obviously it was good for me to play there and get a lot of contact with the ball so it all worked out well and was good."
