The Germany attacker missed Saturday's 5-2 win against West Ham due to a back injury.
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After the triumph, Slot admitted Wirtz would also miss the midweek clash with Wolves.
He stated: "I think that will be too early, but I said last week that I did not expect him not to be available for today, so sometimes in an injury things can develop in a positive way or a negative way.
"Now we are thinking it doesn't have to take too long, but Tuesday will probably be too early.
"The week after will be tight, as things stand now, but as I said, I thought that he would be available for today as well, which didn't happen unfortunately."