The 38-year-old left winger sustained a concussion when he slammed into Philadelphia's Mike Knuble during the third period of New York's 5-3 loss to the Flyers on Saturday.
Shanahan skated toward the bench as Knuble came the other way. Neither player saw the other and they slammed shoulder-to-shoulder. Shanahan went flying backward and struck his head against the ice at 7:27 of the period.
He stayed down for about 10 minutes with his eyes closed. Shanahan was fitted with a neck brace and strapped to a board before leaving the ice.
Rangers coach Tom Renney said Sunday there didn't appear to be any neurological damage. Shanahan left the hospital after a morning examination.
"He saw the neurologist and they are pleasantly surprised with where he is today," Renney said before the Rangers faced the Chicago Blackhawks. "It's not like he can play hockey in the next little while, but they're optimistic with where it sits this morning."
There is no timetable for Shanahan's return to the lineup. Renney didn't know if the veteran of 19 NHL seasons has a history with concussions, but said he wasn't aware of any in recent years.
"Things settled down nicely overnight," Renney said. "It was a huge impact both ways. It'll take some time but we'll pay attention to what they're telling us.
"We'll rely on (the neurologist) and follow the appropriate instructions. So far it's much better."
Knuble broke the orbital bone and cheekbone on the right side of his face in the violent collision. He will undergo surgery in the next few days once swelling decreases.
Shanahan showed no other serious injuries other than the concussion, but is experiencing overall soreness.
"He's got a bit of a bruised shoulder, that's about it," Renney said. "It's like a car accident - everything hurts."
Teammate Aaron Ward spoke to Shanahan on Saturday night and said the two cracked jokes. Ward said Shanahan didn't sound groggy. Renney hadn't yet reached the star forward, who hit the 600-goal mark earlier this season - his first with the Rangers.
Shanahan leads the team with 28 goals.
"I've left messages for him and made it very clear that he doesn't have to call me back," Renney said.
The Rangers didn't immediately make any roster moves, but Renney said Shanahan would be placed on the injured list - keeping him out at least seven days.
New York also lost defenceman Marek Malik during Saturday's game when he reinjured his left shoulder. Malik, who missed three games earlier this month, was to be examined Sunday at Madison Square Garden.
The only bright spot for the Rangers was the return of top goalie Henrik Lundqvist. He was felled early in the second period Saturday when a hard slap shot struck him in the left shoulder in an area not protected by padding.
He finished the period, but sat out the third as Renney chose to rest him because of the back-to-back games.
Every contest is critical for the Rangers, who are fighting to make a second straight postseason appearance. New York entered Sunday's game in 11th place in the Eastern Conference, three places and five points below the playoff cutoff.
"That game is over with," Renney said of Saturday's loss. "We can't dwell on things that are going to stop us from moving forward. We've had enough time to think about it, hopefully they're over that. We have to go out and play the Chicago Blackhawks."