They can only hope it wasn't their last.
The 39-year-old former NBA MVP returned Sunday night after missing more than two months and scored six points in 5 1/2 minutes to help Celtics beat the Detroit Pistons 101-90. But O'Neal left in the second quarter with a new injury that raised new questions about whether he will be able to contribute in the playoffs.
"I don't know what to do, honestly," Celtics coach Doc Rivers said when asked if O'Neal should be shut down for the rest of the regular season. "My inclination is not, because he needs to play. We have to play at full-tilt in six or seven [games]."
O'Neal was not available for comment because he left before the end of the game, Rivers said; TV showed him walking out of the TD Garden with a slight limp. But Rivers expressed optimism because the injury -- explained by the team as a strained right calf -- was not the same as the Achilles' tendon strain that had kept him out since Feb. 1.
"The doctor thought it was very minor. Scary more than anything," Rivers said. "But we'll see."
O'Neal's Achilles' injury was originally described as a minor one that would sideline him for just a few games. Asked how long he thought O'Neal would be out this time, Rivers let out a mirthless laugh.
"I don't know, is the answer," he said. "I don't think very long."
Paul Pierce scored 22 points and Rajon Rondo added 14 assists for the Celtics, who remained one-half game behind Miami in the race for the No. 2 seed in the Eastern Conference playoffs and seemed poised to make a move before O'Neal's new injury.
"He's been out so long, and he tried to do it today without any chance to have any practices," Pierce said. "I just hope he's all right. ... It felt like just having his presence out there was big."
O'Neal entered with 4:43 left in the first quarter to a big cheer from the crowd. He scored on Boston's first two possessions and again later before grabbing a seat for the final play of the quarter.
He returned for the start of the second but he lasted just 49 seconds more before limping off to the locker room accompanied by the medical staff. The team said he would be re-evaluated at halftime; at the break, a Celtics spokesman said he would not return.
"He'll be OK. Shaq's always going to be all right," backup Glen "Big Baby" Davis said. "He doesn't get hurt. Shaq is invincible, man. That's what I believe in. He'll be back. Man of steel. That's what I've been believing since I was a little kid."
The Celtics had been counting on O'Neal to take important minutes at center in the playoffs -- especially after trading Kendrick Perkins to Oklahoma City for Nenad Krstic, who is day-to-day with a bone bruise in his right knee. Backup center Jermaine O'Neal has had injury problems of his own, playing in just 20 games this season.
"We have to have one of the O'Neals," Rivers said. "And then Krstic has to be healthy. If we have that, we have size."
A 15-time All-Star and four-time NBA champion, O'Neal signed with the Celtics for the veteran's minimum salary last summer for the chance to win another title. He has been limited to 37 games this season and is averaging 9.3 points.
He missed a week in November with a bruised right knee, a week in December with a calf injury and another in January with a sore right hip. He returned for three games -- a total of about 34 minutes -- before missing the next 27 games with what the team officially has called a sore right leg.
The Pistons led by three points at the end of the first quarter and led 39-38 with 4:29 left in the second before Boston scored the next 11 points to take a double-digit lead. Detroit answered with a 9-0 run of its own to make it a one-point game, 49-48, at the half.
But Boston scored 13 straight points in the third quarter, starting with a 3-pointer and dunk by Pierce, and ending with Garnett's dunk on a feed from Delonte West that made it 80-64.
"They're a veteran team that understands how to finish games," Pistons coach John Kuester said.
West tried an alley-oop in the second quarter, but he threw it too hard and it bounced off the backboard and through the net for a 3-pointer. ... The Pistons have lost 50 games in consecutive seasons for the first time since 1993-94 and '94-95. They need two wins in their last six games to avoid last year's total of 55 losses. ... Pistons guard Rodney Stuckey did not play. Kuester called it a setback in his "growing process."