At the moment it is known that he has a hamstring injury and if it is just a bruise/sprain, then he will miss the last game of the group stage and then return to action again. If this is a tissue rupture, then the consequences will be much more serious and he will miss more games (including in Liverpool). I would like to see how Klopp reacted to this news when he was told - it was probably something emotional, like how he behaves during games 
I believe it was only a precautionary step to avoid a hamstring injury; he walked out of the pitch by himself, so I don't think it was serious, and if it was, he wouldn't be hopping and moving from angle to angle motivating his teammates the way he did yesterday with such enthusiasm. The last game is important he might risk it. Klopp must have called him since yesterday, pleading with him to take the risk and skip the final group game. They have a league to chase and would prefer not to lose Salah to a long-term injury.
Despite knowing that Arsenal has drop form, I can't still say that Crystal Palace can get their way out of the game. With this their current form, Arsenal is still doing better than Crystal Palace on the pitch. For anyone who is always watching Arsenal games, they will know that Arsenal is still not that bad, even in their recent game that they lost to West Ham and Fulham. Arsenal was not just lucky in scoring recently; they always created good chances, but creating those chances to goals now is their big problem.
If they continue to rely on Saka and do not sign a proper striker this month, they will create several chances without scoring any.