He immediately fell to the ice in pain, and the game was stopped. He was unable to put any weight on his left leg as he was helped off the ice. Tim Thomas replaced him in net.
Rask had stopped 11 of 12 Islanders shots at that point and left with the score tied 1-1. The Bruins eventually lost 3-2.
Coach Claude Julien confirmed to the media before Sunday's game at New York against the Rangers that Rask was not with the team and will not be making the road trip to Toronto for Tuesday night's game. Julien had no update on the exact injury and after the game the team said a full medical evaluation would not be made until Monday.
"It's really hard to watch," teammate Tyler Seguin said following Saturday's game. "(Rask) is one of the hardest working players on our team with practices and what not and even if he's playing on a game day, he's still taking shootouts after practices. To see a bad bounce like that and see him go down and have to come out of the game isn't something any teammate wants to see."
"I mean as soon as he went down, you know as a goalie, I'm at least coming in right away this game, you never know about things sometimes," Thomas said. "Things could look terrible on the ice and they don't end up taking a lot of time out to recover, or there is a lot of times you don't even see the injury and then it's something that ends up being really long term. So, I don't know, that's not my area."
Also, Daniel Paille suffered an undisclosed injury in the third period and did not return. Paille was not available Sunday, with Julien saying he is day to day.
The Bruins received some good news on the injury front with the return of Johnny Boychuk. Boychuk returned to the lineup from a mild concussion Saturday and felt good for the 20:24 he played in the loss.
"It felt pretty good, just to get back into the groove of things," said Boychuk, who suffered the concussion after a Chris Neil hit in Ottawa last Saturday. "To just get out there and do the simple things."
Boychuk was under strict orders to leave the game if he sensed any symptoms at all, but fortunately that didn't happen.
"They told me if I felt any symptoms at all, then to get off," said Boychuk. "And if I had to sit out another week, it would be fine, because we have enough guys to fill in. But no symptoms at all after warm-ups. And after the first period, same thing, no symptoms the whole game."
Julien was relieved Boychuk came back after missing only two games.
"The most important thing is the fact that it wasn't a long-term thing," he said. "He felt good before the game. He felt good during the game. As far as I know, there haven't been any issues at all. So, hopefully that's the way it's going to continue."
ESPNBoston.com's James Murphy contributed to this report.