West Ham boss Sam Allardyce could hand debuts to as many as five players for the visit of Pompey.
Defender Guy Demel, midfielders Papa Bouba Diop, David Bentley and Henri Lansbury and striker Sam Baldock have all joined since the Hammers' last outing at Nottingham Forest.
Allardyce will not make wholesale changes following that 4-1 win, but Bentley and Baldock could be involved from the start.
Demel will probably be on the bench with Allardyce's back four looking solid, Diop may need to build up his fitness while Lansbury only linked up with his new team-mates on Tuesday following England Under-21 duty.
Abdoulaye Faye (groin) is doubtful, Gary O'Neil and Jordan Brown (both ankle) are still injured but Callum McNaughton is available after a ban.
Portsmouth midfielder Hayden Mullins will be fit to travel to his former club West Ham.
Mullins, who made 213 appearances in six years for the Hammers, suffered a groin injury against Cardiff a fortnight ago but resumed training this week.
Defender Tal Ben Haim returned from international duty for Israel with a sore back but he is also expected to be available, meaning boss Steve Cotterill has a full squad to choose from.
Benjani is pushing for his first start since rejoining the club last month and fellow striker Marko Futacs could be involved for the first time following his recent switch from Werder Bremen.
Veteran defender Christian Dailly has left Fratton Park after his one-month contract expired.