Mac Allister was changed at halftime for Sunday's 1-0 win at Burnley.
Slot later explained: "It is similar to Alex (Isak) but in a completely different way. He missed a lot of pre-season, so he is ready for one game a week, maybe (for) 70 to 90. He played 90 for Argentina and he was really tired after 70.
“He doesn’t have the right build-up towards playing three games a week for 90 minutes, so it was always sure today that I would take him off after 60 minutes for him to be able to be back on the pitch again on Wednesday and for him to be on Saturday back on the pitch again.
“I had already made one substitution in the first half, so if I then take him off at 60 minutes that would be my second one. If I then want to make (another on) 75 then in the end I can do nothing anymore.
“So, that combined with the fact the tackle was a tackle he felt – and I am not surprised by the fact he felt that tackle, by the way – it was a combination of both.
“He said it was fine and good enough to go on, although he limped a lot, so that was more his mentality I think than it was he could actually perform at his best for 15 minutes longer.
“So, the combination of him being injured and me not wanting to lose the second substitution after 60 minutes led to it – and us not playing so well, by the way. Bringing Dom (Szoboszlai) to the midfield, more players that can attack the box. So, a lot of arguments and (it was) partly tactical.”