The Dutch midfielder was forced off with an ankle injury during Sunday’s 2-1 defeat to Manchester United, as he appeared to twist his ankle while challenging Bryan Mbeumo in the second half.
Liverpool have won one and lost one of their two Champions League outings against Galatasaray and Atletico Madrid. Now, they head to Germany where Slot has confirmed that the side will be without Gravenberch is a tough blow to take.
"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."
The 23-year-old has racked up nine appearances, scored two goals, and provided two assists for Liverpool across all competitions this season. Despite his injuries, he has been arguably the club’s best midfielder and without him, Slot’s side look unlikely to bounce back from their poor form.
Liverpool travel to Brentford on Saturday in a bid to get their Premier League campaign back on track before facing Crystal Palace in the EFL Cup in what is a tough run of games for Slot’s side who are in a slump.