Then he made a surprise visit to New York's dressing room about an hour before the club's 2-1 victory over the Chicago Blackhawks.
"It didn't hurt, that's for sure," Rangers coach Tom Renney said. "It was good to see him standing up."
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.
Renney said there were no signs of neurological damage, and 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 Sunday's game. "It's not like he can play hockey in the next little while, but they're optimistic with where it sits this morning."
The biggest surprise was his appearance back in the locker room. Renney got a last-second warning before the star forward showed up.
"It was pretty inspirational to see him come when he is supposed to go right home and just rest," forward Matt Cullen said. "For him to go out of his way and do that shows how much he cares.
"It was really impressive."
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."
Shanahan, who leads the club with 28 goals in his first season in New York, delivered a simple message. He wanted his teammates to know he was thinking about them, and he gave them good luck wishes - expressing his desire to rejoin them quickly.
"He said thank you for all the phone calls he got from the guys, but he didn't remember who called," goalie Henrik Lundqvist said. "It was just good to see him smiling."
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 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 rested him because of the back-to-back games.
After a night of icing the shoulder, Lundqvist made 21 saves for his 25th victory of the season.
"I wanted to get in right away and get a win," he said. "I know it's no problem, it's just pain."
Every contest is critical for the Rangers, who are fighting to make a second straight post-season appearance. New York entered Sunday's game in 11th place in the Eastern Conference, three places and five points below the playoff cutoff.