Farke substituted Gruev for Joe Rothwell in his lineup that were held to a 1-1 scoreline with draw specialists West Bromwich Albion last time out, but on the road, the German may take a more cautious approach.
The Leeds manager is reluctant to play an overtly attacking lineup in away fixtures, prioritising defensive solidity for the most part, which could mean his midfield pairing leaves supporters somewhat disappointed.
However, a starting pair of Gruev and Ao Tanaka did help Leeds deliver victories against promotion contenders Sunderland and Sheffield United recently as Rothwell was deployed from the bench to devastating effect.
Elsewhere in the predicted lineup, Brenden Aaronson's place in the team is up for debate after another display at home to West Brom where the American international failed to score or assist.
Here's how we expect Leeds to start against Pompey.
1. GK: Illan Meslier
A little hesitant for the Pompey goal at the weekend but at this stage of the season, it's hard to see Farke changing his No. 1. | Cody Froggatt/PA Wire
2. RB: Jayden Bogle
Into the final game of his two-match suspension tightrope walk. If Bogle avoids yellow at home to Millwall, it's plain sailing for the rest of the campaign. Farke has said in so many words that the 24-year-old will be starting, too. | Ben Roberts Photo/Getty Images Photo: Ben Roberts Photo/Getty Images
3. CB: Joe Rodon
It appeared to be a miscommunication between Meslier and Rodon for the Portsmouth goal last Sunday but the Wales international is almost a certainty to be involved from the start in midweek. Photo: George Wood
4. CB: Pascal Struijk
Vice-captain and skippering the side in Ethan Ampadu's absence, Struijk's name is one of the first on the teamsheet. Part of the league's best defence, aside from Burnley, it's hard to make a case for sweeping changes at the back, given the limited options to replace him. Photo: Gareth Copley
5. LB: Junior Firpo
Probably his most consistent season as a Leeds player, Firpo has been a regular threat down the left flank, steady at the back, worked well alongside whoever the left-sided centre-back has been and should retain his spot for the remainder of the season with few complaints about that from the stands. | Danny Lawson/PA Wire
6. CM: Ilia Gruev
Not his best showing at Fratton Park but Farke has defended the Bulgarian in his pre-match press conference since that match, which suggests he'll persevere with the holding midfielder against Millwall. | George Wood/Getty Images Photo: George Wood/Getty Images