While talking up the prospect of Isak making the bench on Friday, before today's kickoff at the Etihad, Slot announced Isak wasn't in the matchday squad.
He said, "I was hoping the same thing, that Isak would join the bench today, but you always make these decisions in collaboration with the medical staff, the player staff and the player himself.
"We came to the conclusion that it was better for him to have a couple more training sessions than just one or two, and then immediately jump into a match like this one where there may be extended playing time.
"The situation now is that I hope he is available on Wednesday (against PSG for the first-leg of the Champions League quarterfinal), but today was too early for him."
Isak returned to Liverpool training on Thursday for the first time since suffering a serious leg fracture before Christmas.