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...
1. Goalkeeper - Craig MacGillivray
The keeper's stoppage-time heroics ensured Pompey didn't surrender three points at Oxford on Tuesday. He'll be aiming for another clean sheet. Photo: PinPeP
2. Right-back - Callum Johnson
The defender delivered another classy performance at Oxford and is as important to Pompey's promotion push as any other player. Photo: Joe Pepler
3. Centre-back - Sean Raggett
Helped Pompey keep a clean sheet at the Kassam. He'll be in for an aerial battle against a robush Gillingham strike force. Photo: Joe Pepler
4. Centre-back - Rasmus Nicolaisen
Delivered another good performance at Oxford and caught the eye with his passing. Keeping Jack Whatmough out of the team. Photo: Graham Hunt