Kerkez was changed at halftime of the 3-2 loss at Dean Court.
Slot insisted afterwards: "No, there was not an injury and I wouldn't say it was tactical. It was obvious already before the game that it was not smart to play him another 90. There is a lot to be said about the players I constantly play and I have to keep them fit, I have to manage their load.
"It was yesterday when the performance staff came to me and said if we would have had an extra day he wouldn't have trained yesterday to recover a little bit more. So then you are always in a certain risk zone and I already had to make a substitution in the first half. So that means if you leave him on and you take him out at 60 minutes, your second substitution is left.
"So that is why I decided to take him off at half-time because it was always the intention to take him off somewhere in the second half. I did it now a little bit earlier."
Meanwhile, Slot snapped back at reporters asking about the future of fellow left-back Andrew Robertson with a move to Tottenham now being discussed.
He replied: "What do you think my answer is going to be? Have I ever said anything about transfers in front of these microphones? My answer is always the same and it's quite boring to always give the same answer... we don't talk about transfers in public."