PHILADELPHIA -- After the Philadelphia 76ers were routed on their home court by their rivals, the Boston Celtics, to open the second half of the season Thursday night, a dejected Joel Embiid said he needs to "fix the problem" in his left knee to return to his All-Star form.

Embiid didn't look like himself Thursday night, scoring 15 points on just 3-for-9 shooting from the field in 27 minutes. The nine shot attempts were Embiid's fewest in a game this season in which he didn't leave early because of an injury or ejection.

The issues with Embiid's knee, combined with a foot sprain, have caused him to play in just 18 of 55 games for the Sixers (20-35), who remain tied for the sixth-worst record in the NBA after the Brooklyn Nets also lost.

"The way I was playing a year ago is not the way I'm playing right now," Embiid said after a 124-104 loss to Boston. "It sucks. ... I probably need to fix the problem, and then I'll be back at that level. But it's hard to have trust when you're not yourself."

Embiid played so poorly despite having more than a week off due to the All-Star break, adding to the concern. He said the time off helped "a little bit," but he still wasn't himself.

"I'm OK," he said. "Still managing it. Got to keep going and hope for the best."

The Celtics (40-16), winners of eight of their past nine games, made 11 of their first 16 3-pointers and scored 72 points in the first half. They reached 100 points after three quarters.

Boston looked like a team preparing for a deep playoff run and hoping to defend its title. The Sixers looked like a team that will struggle to make the play-in tournament, and likely won't be a factor in the playoffs.

The Sixers are also dealing with the health struggles of Paul George, who confirmed last week's report from ESPN's Shams Charania that he has been getting pain-killing injections to allow him to play in recent weeks.

"I'm hanging in there," said George, who had 17 points in 29 minutes Thursday. "I'm just trying to give this team everything I have.

"The report is true. I'm taking some sorts of medicines to kind of, I guess, play through pain. But yeah, I'm going to try to give everything I got."

After Thursday's loss, Tyrese Maxey said the team's issues come down to effort and trust.

Everything for the 76ers, though, begins and ends with Embiid, who was on pace to be the second player -- and the only one since Wilt Chamberlain 60 years ago -- to average more than a point per minute in a season. That version of him, though, currently doesn't exist.

In the meantime, Embiid said he can still make a positive impact, even if he knows he is capable of more.

"I'm not as dominant as I was a couple of months ago, but that doesn't mean I still can't have a lot of impact on the game," Embiid said. "Just me being out there, I think, helps a lot. My presence, my ability to attract double-teams, get guys more shots.

"It's just tough because you know you can do so much more. But there's no excuses. It's just the way it is. You just have to find ways to figure it out and get better."