A pool of blood was left on the ice near the Canadiens' blue-line after Eller was caught with his head down on an open ice hit by Gryba midway through the second period.
The Canadiens said Eller, who tried to get up before being taken off the ice on a stretcher, would spend the night in hospital.
Eller took a pass up the middle from Canadiens defenceman Raphael Diaz and had just touched the puck when Gryba made contact.
Gryba, who was given a major penalty for interference and a game misconduct, felt the hit was clean.
"I stepped up to make a hit. I kept my shoulder down. He received the puck by the time I hit him. I saw the replay. My elbow was down and there was no intent to hurt him whatsoever and I hope that he's OK," Gryba said after the game. "I'm not out here to hurt anybody and it's never good to seeing anything like that.
"I hope he makes a full and speedy recovery."
Earlier in the period, Canadiens defenceman P.K. Subban caught Ottawa forward Chris Neil with a spectacular open ice hit, but the Senators veteran was not hurt.
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