The midfielder was withdrawn during the second half of Liverpool’s 2-1 defeat by Manchester United at Anfield as a result of a twisted ankle.
Gravenberch was then not part of the Reds’ travelling squad on Tuesday for the Champions League fixture at Eintracht Frankfurt on Wednesday night.
Speaking to Liverpoolfc.com, Slot said of the No.38: “Yeah, I had to take him off during the weekend because he limped a little bit, as we could all see. So, unfortunately, he’s not ready to play tomorrow.
“That already means I definitely have to change one player and with him not being there, that might mean something for others as well, because he has such a particular quality in our squad, which we’ve seen when we played Bournemouth for example, when we played the Community Shield – that we missed a little bit of a player that was always protecting our back four.
“Ryan is not available for the Frankfurt game, hopefully he will be available at the weekend.
“But it’s an ankle injury, we have to wait and see, give him a bit of time and see where he is when we come back from Frankfurt.”
