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...
17. Sub 6 - Jordy Hiwula
Fans will likely continue to ask for the striker to be given more game-time after being handed just three substitute appearances in the league since arriving in October. Photo: Joe Pepler
18. Sub 7 - John Marquis
Will have to be patient for another start and a goal off the bench would do his confidence good. Photo: Joe Pepler