Kassian's suspension will include the last three preseason games and the first five games of the regular season.
Kassian received a double minor on the play during Saturday's game. Gagner suffered a broken jaw and didn't return. He will miss the start of the regular season.
"I had no intention of slashing him in the face," Kassian said Monday after his hearing with NHL disciplinarian Brendan Shanahan, according to TSN. "It was definitely accidental and hopefully he gets back sooner than later."
Gagner shared news of his recovery on Twitter Monday night, writing: "Thank you all for the support. Excited to come back stronger and hopefully better looking than a few days ago."
Weise will sit out the remaining three games of the preseason but is eligible to return for the regular season.