The Sabres say Eichel will be healthy and ready to play in time for the start of the 2021-22 campaign.
Sportsnet's Elliotte Friedman reports the 24-year-old needs surgery to address the injury and is expected to undergo a procedure soon.
Eichel hasn't played since a March 7 loss to the New York Islanders.
The star pivot struggled in 2020-21, like most of his teammates on the lowly Sabres, recording just two goals and 18 points in 21 games.
Eichel was coming off a pandemic-shortened 2019-20 campaign when he produced at a career-best 1.15 points-per-game clip and put up 78 points in 68 games.
The news comes amid a disastrous season for the Sabres — who sold off top players like Taylor Hall, Brandon Montour and Eric Staal ahead of the trade deadline — and are all but assured of matching the NHL playoff drought record of 10 seasons.