Elliotte Friedman of Sportsnet reported Wednesday that Eichel, who last played March 7, will have surgery "soon" so he can begin recovery and preparations for next season.
The 24-year-old Boston University product is one of the NHL's most dynamic offensive talents when healthy. He's recorded 355 points (139 goals and 216 assists) across 375 games since the Sabres selected him with the second overall picks in the 2015 draft. He tallied two goals and 16 helpers in 21 appearances this season.
Eichel has remained mostly durable during his time in Buffalo. His absence because of the upper-body injury marked his first extended time out of the lineup since suffering a high-ankle sprain in back-to-back seasons (2016-17 and 2017-18).
Sam Reinhart should continue to serve as the team's top-line center after shifting over from right wing. It could also lead to more opportunities for the resurgent Casey Mittelstadt in offensive situations.
Eichel is a critical piece of an otherwise struggling Sabres offense. It always made sense for the team to play it safe with its captain following his latest injury since they fall well short of the contender category again this season and he remains a foundational cornerstone for the future.