Ference went unpunished in the first period of Boston's 4-1 playoff win Wednesday night when he elbowed Grabovski in the head by the boards.
The NHL said it was reviewing an illegal check to the head.
Grabovski finished the game.
Asked about the hit after the game, Boston coach Claude Julien said he hadn't seen it and couldn't comment.
Toronto coach Randy Carlyle said it was part of the "physicality" of the playoffs.
"It's a game that's made to be physical," he said. "You're allowed to hit people.
"To judge if it was offside, a bad hit, or a belligerent hit, that's not for me to judge. That's for people in the league to make those determinations."