Henderson was withdrawn at half-time in Saturday's 1-0 win over Huddersfield Town with a hamstring problem, while Keita is also recovering from a hamstring issue suffered on international duty earlier in October.
On the former, Reds boss Jurgen Klopp told Chris Shaw for Liverpool's official website: "It's not too good, to be honest. It's nothing we have to worry too much about, but it's a hamstring issue so we will have to see. He will not be available for tomorrow for sure, and probably not Cardiff [City], but hopefully then he can be back. We will see."
On Keita, the German added: "Naby is already outside running, but the game tomorrow will be too early for sure."
Sky Sports News shared more of the coach's comments:
Sky Sports News @SkySportsNews
👍- Sadio Mane in contention ❌ Naby Keita and Jordan Henderson ruled out Jurgen Klopp offers an injury update ahead of @LFC's @ChampionsLeague League match against Red Star Belgrade tomorrow night... Read the full article here: https://t.co/bPsXwHTSGO https://t.co/t2vxaLvi9C
Henderson knits things together for Liverpool in midfield, while Keita helps drive play forward and can link up with the forward line.
Missing both players is a blow, particularly as the Reds lacked fluidity in their clash with Huddersfield.
Given both will be absent, it may give supporters the chance to have a closer look at one of the team's other summer acquisitions, though, as the Mirror's David Maddock noted:
If Fabinho is given the nod, he'll likely be tasked with protecting the back four, with Georginio Wijnaldum or James Milner asked to provide some creativity further forward.
It's vital Liverpool collect six points from their matches with Red Star while group rivals Napoli and Paris Saint-Germain square off, and the Reds can't afford to drop points at home after losing to the Italian side in their last Champions League outing.
Liverpool should be capable of securing a win over Red Star at Anfield even without Henderson or Keita, but their absence is hardly ideal.
In their stead, Fabinho—who has made just four appearances this season—can stake a claim for more minutes if he's given the chance.