The duo joined Liverpool's debilitating injury list for the weekend loss to Fulham, although both injuries are thought to be relatively minor and they will be assessed ahead of the trip to Budapest.
Of the two, Kabak is the most likely to be available having returned to training on Tuesday, while Firmino was absent for that session and so could miss out again on Wednesday.
Firmino and Kabak were two of seven players to make way against Fulham as Jurgen Klopp rang the changes - partially to introduce fresh legs and also no doubt with one eye on this Champions League tie, which has grown in importance which each passing Premier League defeat.
Trent Alexander-Arnold, Fabinho, Thiago Alcantara, Sadio Mane and Curtis Jones were the others to lose their places, and all five will be hopeful of a return to the starting XI on Wednesday, although in midfield Naby Keita will be eager to keep his spot against his former club.
Fabinho came off the bench to play in midfield towards the end of that Fulham clash, and he could return to his more natural position for this game if Kabak is deemed fit enough to start.
Nathaniel Phillips was not included in Liverpool's Champions League squad for the group stages but has now been added to their roster, so he is free to start on Wednesday.
Joel Matip, Virgil van Dijk and Joe Gomez all remain sidelined, as does captain Jordan Henderson, but Liverpool are now almost back up to full strength as far as attacking personnel is concerned with Diogo Jota making his first start since December at the weekend.
If Firmino is passed fit then Klopp must decide whether to stick with Jota or recall the under-performing Mane and Firmino, the latter of whom is in an exclusive club alongside Lionel Messi and Kylian Mbappe as the only players in double figures for both goals and assists in the Champions League since the start of 2017-18.
Mohamed Salah was the only one of the usual front three to start at the weekend, and he will expect to keep his place as Liverpool's top scorer this season, with one of those goals coming in the first leg.
Indeed, Salah is now Liverpool's all-time leading scorer in the Champions League with 23 in 40 outings, and a brace would see him become the second-fastest player to reach 25 goals for an English club in the competition, behind only Ruud van Nistelrooy for Manchester United.
Liverpool possible starting lineup: Alisson; Alexander-Arnold, Phillips, Kabak, Robertson; Thiago, Fabinho, Wijnaldum; Jota, Salah, Mane