He is considered day-to-day with an upper-body injury. It could be simply that Andreas Athanasiou is banged up and was trying to play and grind through it. They may have shut him down knowing that the holiday break was coming, and it allowed nearly a weeks rest for the forward. It could be that the Detroit Red Wings are so banged up it is hampering his effectiveness and they wanted to give him a rest.
Let us put all of that aside for a moment. Good players find a way. The do not shrivel up and disappear when things are not going well.