The Celtics are "going forward as if the affable center won't be returning to [the] team for the playoffs," according to a report by Bill Burt in The Lawrence Eagle-Tribune.
The report says that O'Neal could not complete one sprint at practice on Saturday, as he tries to recover from calf and Achilles injuries.
"If he were to come back, it would have to be a miraculous recovery," an anonymous source told The Eagle-Tribune. "And at his age and physical condition, the Celtics have planned accordingly."
Since Feb. 4, O'Neal has played in just one game. He was expected to perhaps be ready to return for Game 1 of the Celtics' first-round series against the Knicks, but he's been inactive in both games thus far.
On Saturday, Celtics president of basketball operations Danny Ainge discussed the setback, without mentioning the specifics.
"We tried to get him out there in practice [Saturday], just to simulate a game as much as we could," Ainge told reporters at the team's facility in Waltham, Mass. "He's not ready. We don't know when he'll be ready. We'll just keep evaluating from day to day."
Team physician Brian McKeon said the only remedy for O'Neal's injury is time, but it's not known how much is needed.
"I was telling Danny and the coaches that in the last 20 years, this is one area of medicine where we've made no progress," he said on Saturday. "It's just time. It's just hard to get enough healing potential in that area."