Watford captain John Eustace comes back into contention.
The midfielder has missed the club's last three games with a back injury but has used the international break to regain his fitness.
However, influential defender Lloyd Doyley has not progressed as quickly with his recovery from a thigh problem and remains a doubt against Pompey.
Michael Kightly missed the 1-0 defeat at Middlesbrough last time out with a recurrence of his hamstring injury but has trained and is in contention, while fit-again loan striker Craig Beattie replaced the winger on the bench at the Riverside.
Centre-back Martin Taylor remains in the treatment room as he continues his rehabilitation from collarbone surgery, while midfielder Stephen McGinn is also battling back from his long-term knee injury.
The Hornets will be looking to get back to winning ways after defeat to Boro ended a welcome run of back-to-back victories against Peterborough and Brighton, both of which came at Vicarage Road.
Liam Lawrence remains an injury doubt for Michael Appleton's first game in charge of Portsmouth.
The midfielder missed Pompey's win over Nottingham Forest a fortnight ago with an ankle injury which also forced him out of the Republic of Ireland squad.
If Lawrence is unavailable, Appleton could stick with the side which beat his predecessor Steve Cotterill's Forest 3-0.
Striker Benjani returned from a hamstring injury as a late substitute and should be involved again, while youngsters Lewis Tallack and Lewis Stockford are back from loan spells in non-league.
Defender Hermann Hriedarsson is having treatment on an Achilles problem and loanee Bjorn Helge Riise, who was on the bench against Forest, has gone back to Fulham.
