Steven Caulker is a doubt for City.
The on-loan Tottenham defender was forced off after 34 minutes of the 4-1 victory at Coventry on Saturday with a recurrence of the hip problem that saw him substituted in the previous game against Scunthorpe.
"It is one we looked closely at and the medical people told me he was fine to play. He had a fitness test before the game and his movement was fine," said City manager Keith Millen.
"But he had a bruise on his hip and, if you get a whack on it, then you are going to be sore. It was a bit of a gamble and the lad was happy to play, but I don't think he has made it worse or done any long-lasting damage.
"Damion Stewart came in and won everything in the air and he can step in against Portsmouth if Steven is not ready."
Midfielders Jamal Campbell-Ryce and Lee Johnson and strikers Brett Pitman and Andy Keogh are also available for recalls.
Pompey boss Steve Cotterill has no new injury or suspension problems ahead of the trip to Bristol.
Midfielder Hayden Mullins and utility player Joel Ward were major doubts ahead of the game against Sheffield United at the weekend with calf problems but both started, with Mullins lasting the full match and Ward coming off after 71 minutes.
Cotterill employed Ward in an unfamiliar position behind lone striker Dave Kitson in the 1-0 win against the Blades and it remains to be seen whether he sticks with the youngster or opts to start with veteran forward Kanu.
Aaron Mokoena is pushing for a starting role after some impressive performances off the bench in recent weeks.
Midfielder Liam Lawrence continues to be sidelined with a calf injury that is expected to keep him out for another two or three weeks.
In-form Pompey are looking for a seventh straight win and a seventh clean sheet on the spin.