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...
13. Sub 2 - Jack Whatmough
The academy product is stll trying to win back his starting spot since returning from suspension three games ago. Photo: Robin Jones
14. Sub 3 - Charlie Daniels
Will have to wait for his next chance after starting the previous five games before Oxford. Photo: Jason Brown
15. Sub 4 - George Byers
The Swansea loanee's only started once since arriving in January and will be desperate for another chance. Photo: PinPeP
16. Sub 5 - Marcus Harness
The mercurial winger was subdued at Oxford and may be given a breather. Photo: Joe Pepler