Many fans were surprised when they saw that Kachunga was not even part of the 18-man squad for the game.
The 26-year-old is working his way to full fitness after suffering a knee injury last season. And his manager says he was excluded due to competition for places within the squad.
"We were very happy that Kacha was, more or less, able to have a complete, full pre-season – we hadn't expected he has been able to train with us more or less the whole period," said Wagner to The Huddersfield Daily Examiner.
"But, to be totally honest, this is part of the competition.
"We were able to see he was out for, more or less, half a year and he isn't on his best form – but he can't be after he was out such a long period.
"We will try and support him and help him to come on form as soon as possible and this is the nature of progression – the competition gets bigger and stronger.
"You have to be there every single week and every single training session – this is why we select the squad and why we select the starting XI.
"At the end, though, everyone has the chance to get qualified for the starting XI or for the squad and this is, for sure, a little bit different this season.
"Everyone knows they are not untouchable, but I know the guys will fight and work for their shirt."