Salah and Wataru Endo joined the Reds in midweelk for a first preseason under new manager Slot.
The Dutchman told the club's website: "Mo came back strong, he was really fit. That’s what I think he always has been but it’s the same this year.
"What you want from them, like I said, is to set the example for the youngsters as well. For them, it’s very important – just like the other ones from the first team – that they stay fit.
"They are full of energy and that’s the most important thing at the moment; keep them fit, build it up from there and try to teach them as much as we can."
Slot also said: "I’m enjoying it a lot. The pitches are great. The boys are full of energy; Pep (Lijnders) and Jürgen (Klopp) already said to me last season that I’m going to enjoy working with them – and they haven’t lied at all. Full of energy.
"Also the youngsters coming from the Academy, they have the same intensity and the guys are open to learn. The way I see it, the way I feel is that they enjoy them (the sessions) as well. So, the three most important ingredients."