Casey Mittelstadt was placed on injured reserve on Thursday and could be out long-term for the Sabres with an undisclosed injury.
The forward left in the third period of a 2-0 loss to the Anaheim Ducks on Tuesday.
"Casey is going to see a specialist today so we'll have information after that," Sabres coach Don Granato said Thursday. "We'll wait until we have the information from the doctor he sees today to see what the next step is."
Mittelstadt, who has one goal in three games, missed 21 games earlier this season because of an upper-body injury.
"Obviously another injury," forward Dylan Cozens said. "It's disappointing to see and we all feel really bad for him. We know how exited he was to finally come back into the lineup and to be out again, it's tough."
Granato also said goalie Malcolm Subban, who was injured in his Sabres debut on Saturday, is progressing.
"He had another good day this morning," Granato said. "I'll talk to our training staff after the players clear out here and see where he sits here after today."
Buffalo hosts the New York Rangers on Friday.