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 
Klopp said he had contacted Salah and he felt from the injury but the diagnosis has not yet been made whether there is a tissue rupture or a slight bruise like this is still being followed up by the medical team.Maybe Klopp will be a little nervous to hear this news because Salah is one of Liverpool's key players in producing goals if he is absent for so long then it is a loss for Liverpool there is no wing stick pillar as great as Salah so that is what is worried about.
Now there are too many rumors that he will be out longer, currently there is no clear confirmation but the injury is definitely Salah's now.
I remember that last season Klopp complained more than anyone (and he started it before anyone) about the busy calendar due to the World Cup and the fact that the players could not withstand such a load (more susceptible to injury), now after Salah’s injury and his potential retirement long term Klopp will probably become a hater of national team games
It is noteworthy that in 6 years in Liverpool, Salah missed only 10 games due to injuries. This stability is impressive. Will he be able to maintain the same level now that he is already 30+