He explained his decision to substitute Mabaya, who had entered the match from the bench in the first-half, citing the player's yellow card and the match’s physical intensity.
Slot acknowledged the disappointment for Mabaya, but praised the youngster after their shock FA Cup exit at the hands of Plymouth.
Slot stated: “I think it is a fantastic moment for every player to make your debut and for him as well. But I felt I had to take him off for two reasons. He was already on a yellow and it was a game with a lot of duels and a lot of intensity and that's their playing style.
“They bring a lot of long balls in, so if you're one time wrong then it's a yellow again, and it was a game that was hard enough with 11, let alone with 10.
“And I felt we needed to make an offensive substitution and the other three were Jarell (Quansah), Wata (Endo) and Kostas (Tsimikas) and that didn't seem smart to me to take one of these three off. I took that decision, and I thought I had to tell him because making your debut and then to be taken off after an hour or something like that is very disappointing for him of course."