The Blues will be aiming to pull off an upset against the Premier League hosts at the Amex Stadium.
Kenny Jackett has to weigh up the starting line-up against the Seagulls, with a League One trip to Rochdale on Sunday to also plan for.
The boss has said he wants some continuity, though, as he looks for Pompey to get into a winning rhythm.
Here's how we think the Blues could start...
13. Sub 2 - Cameron Pring
Challenging Lee Brown for a starting spot and wouldn't be a big shock if he started Photo: Sarah Standing
14. Sub 3 - Bryn Morris
Should be fit after picking up a hip injury against Shrewsbury but may not be risked to start. Photo: Joe Pepler
15. Sub 4 - Andy Cannon
Impressed when coming off the bench this season and is pushing for a starting spot. Capable of featuring in the No10 role or slightly deeper. Photo: Joe Pepler
16. Sub 5 - Marcus Harness
Could be handed a rest ahead of league clash at Rochdale. Capable of causing problems to Brighton's defence if he does feature. Photo: Joe Pepler