The 25-year-old rookie forward was cut by the skate blade of Devils forward Jesper Bratt at 9:20 of the third period and left the game.
Mikheyev is expected to make a full recovery; he will remain at University Hospital in Newark, New Jersey, for further monitoring before returning to Toronto.
"First and foremost, we're thinking about [Ilya]," Maple Leafs captain John Tavares said after the game. "It was obviously scary, seeing that much blood. He's a guy we care deeply about and was having a great night, playing tremendous for us, so thoughts are with him."
Signed as a free agent by the Maple Leafs on May 6, Mikheyev has 23 points (eight goals, 15 assists) in 39 games this season, including a first-period goal Friday.
Maple Leafs defenseman Jake Muzzin is week to week because of a broken foot sustained against the Devils.
Muzzin, who was acquired in a trade with the Los Angeles Kings on Jan. 28, has 13 points (three goals, 10 assists) in 38 games this season.
The Maple Leafs lost to the New York Rangers 5-4 in overtime on Saturday to end a six-game winning streak.
