The league's department of player safety issued the ruling after conducting a hearing with Larsson on Friday, a day after Buffalo's 4-2 loss to the Panthers. Larsson was already facing a one-game suspension after being issued a 10-minute match penalty and five-minute cross-checking major for his hit to Trocheck with 35 seconds left in the game.
The hit occurred after Trocheck and Sabres defenseman Jake McCabe got their sticks up during a skirmish at the Panthers blue line. Larsson skated toward Trocheck and cross-checked him.
In its ruling, the NHL noted Larsson's stick initially hit Trocheck high on the left shoulder before riding up to connect with the player's cheek. The league, however, noted players are responsible for their sticks.
"When a player attempts to intentionally use his stick to deliver a blow to an opponent, he cannot necessarily be excused of all responsibility when the blow lands in an unintended place," the league ruled.
Following the game, Larsson said he merely "pushed him a little bit and the ref came and grabbed me."
The fifth-year player will lose close to $15,900 in salary and miss Buffalo's home games against St. Louis on Saturday and Anaheim on Tuesday.
Emotions boiled over between the Sabres and Panthers shortly after Florida's Colton Sceviour closed the scoring with 2:24 remaining. Officials issued a total of 56 minutes in penalties to six players, including Larsson, over the final 2:01.