Eaves was circling the Pittsburgh net midway through the second period when he took a stiff check to the head from Penguins forward Colby Armstrong, knocking him hard to the ice. While Eaves lay prone, Senators forward Dean McAmmond fought with Penguins forward Maxime Talbot.
Eaves was alert, and was shown speaking to doctors and flexing his hands as he was wheeled off the ice. One media source reported Eaves had movement in all his extremities, and was diagnosed with a concussion.
His status for Game 4 on Tuesday was not certain, but a concussion would likely keep him out.
"I thought it was a dirty hit," Ottawa's Jason Spezza said following his team's 4-2 victory. "Any time a guy takes a run like that ... obviously, there is some intent there."
Senators coach Bryan Murray disagreed with his player.
"The kid was trying to make contact," Murray said. "He (Eaves) had his head down a little bit. He drove with his shoulder, that's part of hockey. I feel read bad with him getting hurt, and I know there will be extensive articles about ... how that shouldn't be allowed. It was a fair hit, a hockey hit, and we live with that."
Senators goalie Ray Emery said the sight of seeing Eaves hurt may not have helped his teammates build the lead, but possibly prevented them from losing it. Ottawa led twice in the third period Saturday, but ended up losing 4-3.
"I think you kind of dig a bit deeper when you see one of your guys go off on a stretcher like that," Emery said. "It's something you don't want to see and maybe it's something you can rally around."
Armstrong wasn't given a penalty on the play. The Penguins forward was involved in two similar plays this season. On Oct. 14, Carolina forward Trevor Letowski was knocked unconscious and sustained a concussion when Armstrong put a blind-side hit on him in the Hurricanes' end.
Letowski, who also sustained facial cuts, missed nine games because of the concussion.
On Feb. 1, Armstrong put a hard hit on the Canadiens' Saku Koivu near the end boards but also wasn't penalized, though Montreal's Sheldon Souray immediately went after Armstrong. A day later, Canadiens coach Guy Carbonneau labelled Armstrong's hit "a cheap shot."