Bristol City boss Keith Millen is expected to stick with the same side that beat Leicester in midweek.
That means no place for veteran goalkeeper David James against his former club. The 41-year-old was dropped to the bench against Leicester in favour of Dean Gerken.
The game is likely to come too soon for Liam Fontaine who only returned to training on Thursday.
The 25-year-old defender has not played since the Robins' 3-0 opening day defeat to Ipswich after suffering an ankle injury.
Louis Carey will also miss out despite recovering from illness.
The 34-year-old defender boasts the second highest number of appearances for the club but is yet to make an appearance this season.
Benjani could start his first game for Portsmouth since January 2008.
The veteran striker, back with Pompey via spells at Manchester City, Sunderland and Blackburn, made his second 'debut' as a substitute in Tuesday's 1-0 win over Reading.
If he starts, Benjani is likely to replace Kanu alongside midweek goalscorer Dave Kitson in attack.
Norway forward Erik Huseklepp could also be added to the squad if his proposed switch from Bari is completed in time.
Skipper Liam Lawrence has been playing despite an ongoing hamstring problem and should be fine to continue.
Manager Steve Cotterill has no new injury concerns and found himself in the rare position of having to leave players out of his squad on Tuesday with Hermann Hreidarsson and Christian Dailly missing out.