Rask gave up a goal to Chytil, who came charging down the right wing. After he flipped the puck over Rask at full speed, Chytil was hit by Boston defenseman Charlie McAvoy, sending the forward's waist flying into the head of Rask, who was knocked backward hard to the ice.
The club announced Rask's injury midway into the second period. He did not return to the game.
"He's concussed and that's all I know, so he'll go into the protocol, Bruins coach Bruce Cassidy said after his team's 3-2 loss to New York. "Best-case scenario for those is next day he's up and running."
The hit sent Rask onto his back, where he was down for a while before being helped to the bench and down the tunnel to the locker room.
"It was scary," McAvoy said. "He seemed down and out. You saw firsthand the force that the guy went right into him. It didn't look good right away. I just wanted to make sure he was OK. He came back to and we got him off the ice. Just hopefully he's feeling all right."
Rask, 31, entered the game tied with Cecil "Tiny" Thompson as the winningest goaltender in club history with 252 victories and was 6-0-1 in his previous seven starts. Rask had six saves and backup Jaroslav Halak finished with 11.
The Bruins are off until a home game against Winnipeg on Jan. 29.