The suspension is the third in 103 career games for Tkachuk. The 19-year-old is considered a repeat offender under the terms of the Collective Bargaining Agreement and will forfeit $11,280.49.
Tkachuk speared Maple Leafs forward Matt Martin from the bench with 5:53 remaining in the first period of Wednesday's game. He was not assessed a penalty on the play, however.
"That's junior hockey stuff," Toronto coach Mike Babcock told reporters. "He'll learn over time but you gotta give Tkachuk credit -- he played a good game, he played hard. No reason for that stuff."
Tkachuk received a one-game suspension last month for tapping the leg of Detroit Red Wings defenseman Luke Witkowski as he headed to the locker room after a fight. The action ignited a brawl between the two teams, with Witkowski receiving a 10-game ban.
Tkachuk also received a two-game suspension in March 2016 for an elbow to the face of Los Angeles Kings defenseman Drew Doughty.