Chiasson was assessed a five-minute major and a game misconduct. The play occurred after the final buzzer Monday, which the league factored into its decision.
"This is not a hockey play," the league said in its explanation. "This is a forceful, high cross-check delivered to an opponent after the game has ended."
Chiasson had never received supplemental discipline through his 536-game NHL career. The 30-year-old has contributed four goals and seven points through 17 games this season.
The Leafs won Monday's tilt 3-0 and look to sweep the three-game set against the Oilers on Wednesday in Edmonton.