The Celtics said a preliminary diagnosis indicated a "cervical stinger." He was taken to a local hospital for evaluation.
"I can't really disclose that stuff," Pelicans coach Monty Williams said after the game. "We are just praying for his health. He looked like he was OK. I was more worried about his mother. I know she's at home, a nervous wreck, so hopefully she hears this message and is cool with the fact that he's OK and in good hands."
Anderson and Wallace collided near the Celtics' basket with 11:02 to play. They both went to the floor hard.
Anderson remained on his back as he was being checked by the team's trainer and a Celtics' doctor before a stretcher was summoned.
"It was tough," teammate Anthony Davis said. "It's a sad situation. You don't want to see one of your guys go down, especially one of your leaders. We just prayed for him, but at the same time we've got to try and win the game."
After about a five-minute delay, he was put in a back brace and then on a stretcher before being wheeled off to applause from the TD Garden crowd. Both teams came out and surrounded him when the stretcher was brought out.
Anderson had 13 points and seven rebounds before leaving.
"I know what he's going through, the thought process," Wallace said. "I mean, I know the whole process of him lying on the floor waiting on a stretcher to come get you. So my whole thing was just the activity to see him fall, see him moving."
Wallace said Anderson told him he was OK.
"He said he was all right," Wallace said.