The forward was injured Monday by a check from Washington Capitals center Lars Eller late in the third period of a 6-1 win.
"It's going to be at least a couple weeks to three weeks," Hurricanes coach Rod Brind'Amour said Thursday. "That's long for me, so that's not good."
Kotkaniemi scored 26 points (11 goals, 15 assists) in 63 games this season, his first with Carolina. He had an assist in each of his past three games before not playing in a 4-3 overtime loss to the Tampa Bay Lightning on Tuesday.
"The worst part is, you never want to see injuries, but he was really taking a turn, becoming really effective every shift," Brind'Amour said. "The good thing is, you see that, and you know that once he gets back, we will get him up to speed again."
Jordan Martinook replaced Kotkaniemi for a 4-0 win against the Montreal Canadiens on Thursday. Martinook played 11:06 after missing seven games with a lower-body injury.
Carolina (45-15-8) leads the Metropolitan Division by five points over the New York Rangers. The Stanley Cup Playoffs are scheduled to begin May 2.
Kotkaniemi, who could have become a restricted free agent after the season, signed an eight-year, $38.56 million contract with the Hurricanes on March 21. It has an average annual value of $4.82 million.
"You're always weighing the risk versus the reward," Carolina general manager Don Waddell said. "We see a higher projectile (projection) for this player. And as the seasons go on and the [NHL salary] cap continues to go up, we think these kind of players are going to become even more expensive."
