According to a tweet from the Celtics' account on Monday, Daniels left the hospital early Monday morning and was in good spirits.
Coach Doc Rivers was texting with Daniels throughout the day Monday, and said that "as far as life, he'll be OK."
"And that's all that matters to me right now," Rivers said.
Daniels fell face-first to the parquet after the initial injury. After being attended to by team doctors and arena paramedics, Daniels needed to be taken from the court on a stretcher in a scary scene that marred a nationally televised battle of rivals.
"Marquis is doing well," Celtics president of basketball operations Danny Ainge said at a news conference with team physician Brian McKeon on Sunday. "I was just with him at New England Baptist Hospital. He's moving, he's fine. His arms and his legs, everything is fine."
Ainge indicated that Daniels will be sidelined at least one month, possibly longer. While he has regained motor functions, Daniels will undergo a battery of tests, including CT scans, MRIs and serial examinations, in order to determine the severity of the injury.
Both Ainge and McKeon noted that Daniels has experienced spine issues in the past and he endured a similar scare last year in Game 5 of the Eastern Conference finals in Orlando. He was diagnosed with a concussion after that game, but did not suffer one Sunday, McKeon said.
Ainge visited Daniels at the hospital during Sunday's game.
"He just wanted to know the score of the game," Ainge said. "He had talked with his wife and his mother. He was fine."
Asked how the team moves forward, McKeon said the key is simply observation and time, especially given his past history.
"I think he was scared when he was on the court, because he couldn't really move there for a short period of time, so that scared him," Ainge said. "But he's had some issues with this before and some tingling in his body -- his arms and things before."
With 11:01 to play in the second quarter, Daniels posted up on Magic guard Gilbert Arenas, but appeared to snag his neck as he attempted to drive toward the basket. Daniels collided with Arenas' chest and seemed to briefly lose consciousness. Daniels collapsed forward, landing face-first on the floor.
After a long stoppage in play, Daniels gave a thumbs up to the crowd as he was being taken from the court on the stretcher.
Rivers knew immediately there was something wrong as Daniels fell prone.
"Right when he went down, I was already out on the floor," Rivers said. "I don't know who -- Gilbert or someone -- was standing near him and I just told him, 'Don't touch him.' Because you could see it was not good."
Said Celtics captain Paul Pierce: "Obviously when you see a guy lay down there for a [period] of time, you get worried and you pray and hope that he's all right. When we came back to the locker room at halftime, I asked how he was doing and they said he was moving and doing pretty good. I guess he has some type of condition in his neck or spine that I didn't know about. Hopefully he can take some time off, hopefully he can get back on the court, but, most importantly, we're more worried about his health."
The Magic players also were concerned.
"I guess everyone thought he hit my knee or something, but when he turned and faced, I know his neck probably hit [my chest], trying to turn, because I was close to him, and then from there he just hit the floor," Arenas said. "I thought I tripped him or something, so I was trying to pick him up, but [a Celtics player] said, 'Don't touch him because he has neck problems.'"
Arenas said he didn't see or hear anything as Daniels suffered the injury.
"No, he just turned and faced and was trying to go fast, and then 'Boom,' and he just hit the floor. I heard him hit the floor hard. I thought he probably had a little concussion, but, I know Kevin Garnett said, 'Did he hit your knee?' and I said, 'I don't think so.' And then he said, 'He has neck problems,' so sometimes when his neck goes in the wrong [position] he gets paralyzed for a little bit."
"It was scary, man, scary," guard Jameer Nelson said. "I was praying for him. It could happen to anybody. You never want to see a guy get injured and taken off on a stretcher."
Celtics guard Ray Allen isn't sure how the team collected itself because everyone's thoughts were on Daniels.
"I was trying to process what just happened and, when I saw the way he hit the ground, I just started thinking about any time I watched a football game and I saw a guy on the ground, how their body just kind of didn't respond to anything," Allen said. "It looked like he got hit in the wrong spot, where whatever happened to his body he just couldn't move. And when I saw his face, it was the scariest feeling because it was almost like he couldn't do anything. It's the risk we always run, but for that moment it just seemed like, 'Let me go to the hospital and let me do what I need to do to see that he's all right,' because basketball was the last thing on my mind."
Chris Forsberg covers the Celtics for ESPNBoston.com. Information from The Associated Press was used in this report.