Isak completed a £125 million switch from Newcastle United to the Premier League champions on transfer deadline day, bringing an end to a transfer saga that had dragged on throughout the close season.
The 25-year-old has played only 18 minutes this season, with his sole appearance coming off the bench for Sweden in their 2-0 defeat by Kosovo on Monday.
Slot praised Sweden coach Jon Dahl Tomasson for using Isak sparingly and said Liverpool would also manage his minutes.
"We will treat Alex the same as they did. Don't expect him to be every single game 90 minutes on the pitch," he told reporters ahead of Sunday's match.
"That's definitely not going to happen in the upcoming weeks. He missed a proper pre-season, he missed three or four months of team sessions.
"We have to build him up gradually, with us playing so many games, hardly any training time, that's going to be a challenge.
"But we haven't signed him for the upcoming two weeks, we've signed him for six years, so this is what we have to keep in mind and what the fans have to keep in mind..."
Liverpool were also close to signing Crystal Palace defender Marc Guehi on deadline day, but a deal for the England international fell through.
"We would have liked to have signed him, of course," said Slot. "If we feel we can strengthen the team we never hesitate to do so. It's not like all of a sudden we don't have options in that position.
"It's a pity, not only for us but also for the player, I think.
"But he's in a good place, playing for Palace, where he won the Charity Shield and the FA Cup with a very good manager as well. Let's see what the future brings."
Liverpool are top of the league table with nine points from three matches.