We know via the media that Zack Kassian entered the Montreal Canadiens' substance abuse program after he was acquired from the Canucks for Brandon Prust and a 2016-5th round pick on July 1, 2015.
He was involved in a truck crash back in October at around 6 AM on October 4, 2015. The Canadiens/NHL put him in a substance abuse program. He was reinstated to play in the NHL on December 15. The Habs put him on waivers to make him play for St. John's, their AHL affiliate team. He cleared waivers however.