Salah is fit for the tie, says Slot, in his first appearance since announcing he will leave Liverpool this summer after nine years at Anfield.
The manager said: "Is he fit? Yes, he is. Trained y'day and today, he's available. What has happened since he announced it is what he completely deserves. An unbelievable career at this club, every three days, winning trophies, I saw a beautiful picture of him in front of all the trophies he won, so I hope he can add two more before the end of the season.
"A boost? For the club maybe, it doesn't matter for Mo, that is what he has shown, he is always available in his best possible shape and it doesn't change, he has always given everything for this club in all the years.
"I hope he could give even more but that is not realistic because he gave all he had. If we have a Mo in the form he's been in in so many years that will be a big help for us."
Isak return
Slot and Liverpool welcomed Alexander Isak back to training on Thursday. The Swede has been missing since before Christmas after suffering a serious leg fracture.
The Dutchman said: "We'll be too soon to expect him in the starting lineup, first time training yesterday after 101 days out, it will take a bit of time to give him a lot of minutes.
"But we will make sure we do the right thing to build him up but it is a good thing to have him on the training ground, even better to get him on the pitch."
On how he'll use the Swede on Saturday, he added: "It's a difficult one, we don't play a 'normal' game, could go to extra time, which makes it difficult if he can only play 10 minutes.
"We can take him off again of course if we have the players but maybe a few minutes tomorrow but let's wait and see today, how he feels. Two sessions, 100 days out, no sense to start him tomorrow. "
Heavy workload
Reflecting on their form, Slot admits they've struggled for consistency this season. The Liverpool manager conceding they've battled with the workload.
He explained, "We have good players and can play very good football. Every time after a good game, we play 3 days after Real Madrid and that has been the biggest problem this season; so many games, the biggest issue for this team.
"We've shown we have quality players but the amount of games is the biggest issue, so it is interesting to see where we are. We played much better at home and didn't deserve to lose versus City, a big referee decision in that one as well, the (Marc) Guehi tackle on Salah that wasn't a red card, didn't go our way."
Slot then identified Jeremy Doku as a danger man for City.
He continued: "How do we stop Doku? I did my homework well for this game, Doku...the year before he was even better, 11 times he dribbled past one of our defenders, last game was 7/8. I won't be sure he can't do that again but hopefully we learn from that.
"It's not always about Doku, it is the environment, if it's 1v1 then he is one of the best out there, that is a big quality for a team. That can make a difference against low block defences, we have to make sure he is not as isolated against out defenders as he was in the last game and sometimes he was not always on 1v1, sometimes he had the full-back to support him.
"My player, Conor Bradley, had to defend against two players back then."
Facing Man City this season
Expanding further on their clashes with Manchester City this season, Slot admits momentum during the game has been crucial.
He continued: "I think we have felt this season multiple times how important it is to get a lead, we have struggled with that. It's much easier than being 1 or 2-0 up. Scoring goals is vital, so I am happy Alex (Isak) is back. Away game last season, we scored a set-piece, which is so important. We didn't have that at the Etihad last season, they scored, we didn't - had one disallowed.
"First half at Anfield, City dominated the ball, how impressive was it we dominated the ball second half? How many teams do that? So that was a big step forward but we have to show this as well in their stadium, which is harder than 60,000 at Anfioeld giving you the energy you need.
:We have more fans than normal because it is FA Cup and I wouldn't be susprised if we're louder than them."
Alisson out longer
Before signing off, Slot admitted senior goalkeeper Alisson is out for the coming week - including the Champions League quarterfinal first-leg against PSG.
He stated, "Yeah, he will not be part of the PSG game either, out for a bit longer. Towards the end of the season we expect him to be fit."