Kenny Jackett' s side are aiming for successive League One victories following their win at Oxford United on Tuesday.
It was workmanlike but the Blues delivered a much-needed 1-0 success against Karl Robinson’s in-form hosts.
Harvey White bagged his maiden senior goal to cement Pompey’s berth in the play-off places.
And with 17 games remaining, the Blues still harbour ambitions of being promoted automatically.
Jackett now has to ponder whether to go with the same side that beat Oxford or make changes against Gillingham.
Gills chief Steve Evans will be expecting a response from his troops after slamming some of them following their loss to AFC Wimbledon in midweek.
Certainly, it’s a tricky game for Pompey and Jackett will have to get his selection spot on.
Here's how we think the Blues will line-up...
9. Left-midfield - Harvey White
The Spurs loanee was handed a surprise start on the flank at Oxford and bagged his first senior goal. It would be a surprise if he was dropped having helped thicken up the midfield. Photo: Jason Brown
10. Striker - Ronan Curtis
The Irishman made a nuisance for himself after being handed a role up top at Oxford. He'll be hoping more goalscoring chances fall his way, though. Photo: Joe Pepler
11. Striker - Ellis Harrison
His physical presence caused Oxford plenty of problems on his recall to the side and will offer the same against the Gills. Photo: Jason Brown
12. Sub 1 - Lewis Ward
The on-loan Exeter keeper will continue to act as back-up with Alex Bass still injured. Photo: Joe Pepler