The defenseman sustained the injury prior to the Islanders' 2-1 loss to the New Jersey Devils at Nassau Coliseum on Thursday.
"It was just pregame warmup, certainly a freak accident that could have happened to anyone," general manager Lou Lamoriello said. "Unfortunately, it's his Achilles, which will need repair.
"I'm not going to get into what it was, it was in pregame warmups, not on the ice, which they go through naturally every day. It was a freak accident, that's the best way to put it.
"This type of an injury, there is a period of time, certainly it depends upon the healing process, everybody heals different. But this type of an injury, it usually takes around four months."
Pelech has nine points (one goal, eight assists) in 38 games and leads the Islanders with 83 blocked shots. He's second on the Islanders with an average ice time of 21:08, after defenseman Ryan Pulock at 21:55, and played 2:47 per game on the penalty kill, second on the Islanders after defenseman Scott Mayfield (2:50).
Selected by the Islanders in the third round (No. 65) of the 2012 NHL Draft, Pelech has 61 points (12 goals, 49 assists) in 247 games.
Defenseman
Sebastian Aho
was recalled from Bridgeport of the American Hockey league on Friday and could make his season debut against the Toronto Maple Leafs at Scotiabank Arena on Saturday (7 p.m. ET; ESPN+, CBC, SN360, SNO, SNW, SNP, MSG+, NHL.TV). Aho had four points (one goal, three assists) in 22 games with the Islanders in 2017-18. He has 20 points (two goals, 18 assists) in 34 AHL games this season.
"Certainly you're always trying to get better, and you don't replace a player like Adam Pelech at the [NHL] Trade Deadline," Lamoriello said. "It's up to us internally. These are the things that happen throughout the season. It happens to every team. Unfortunately when it happens to you, it hurts certainly a lot more than what you read. But we'll have people now in place who have to come forward."
NHL.com deputy managing editor Brian Compton contributed to this report
