Slot, ahead of tonight's clash with Newcastle United, admits he was unhappy with Nunez's workrate against Wolves and Aston Villa. The Uruguay striker did not get off the bench for the win at Manchester City on Sunday.
"I helped him by saying you can miss a chance," Slot said in his news conference before Wednesday's visit of Newcastle.
"I wasn't only hard on him. But for the second time in a row I wasn't happy with his work effort, against Wolves and against Villa.
"I can't accept if a player doesn't give everything. That is clear. I can accept it once, but twice was a bit too much. That's why I addressed it.
"If you miss a chance, you need to be fighting for the team. I'm not saying he didn't do that at all, but it wasn't the usual Darwin, the one that is loved by the fans. That is mainly because he always works so hard."