Umberger left Saturday's Game 1 double-overtime loss after absorbing an open-ice check from Buffalo defenseman Brian Campbell 12 minutes into the first overtime. Woozy from the collision, he lay on the ice for several minutes before he was helped to the locker room.
Umberger has yet to be cleared to play by team doctors, and a decision on whether or not he is able to dress will be made later Monday afternoon.
Umberger was leveled by Campbell at the Flyers' blue line. He sustained a bloody nose on the play, and a day later complained about having a stiff neck. Umberger took part in the team's morning skate on Monday, and declared himself ready despite having some nasal problems.
"I felt real good out there skating," he said. "I felt fine."
If Umberger can't play, Flyers coach Ken Hitchcock said Branko Radivojevic would take his place.
"He's a significant player of our team," Hitchcock said of Umberger, a 20-goal scorer in the regular season. "We need him in the lineup."
Eager played in 25 games for the Flyers this season, registering three goals and eight points.
"We feel confident in his ability," Hitchcock said. "He has the speed to get up on the attack."
The Sabres have a 1-0 lead in the series after winning the first game 3-2 on a double-overtime goal scored by center Daniel Briere.