James underwent an MRI that revealed "general swelling," Lakers coach Frank Vogel said. Sunday was the third straight game that James, 37, had missed because of the knee.
"As long as the swelling is there, he's going to be out and we'll get him back as soon as we can," Vogel said.
Prior to the knee soreness and swelling, which Vogel said was not caused by a specific play but rather something James woke up feeling in Philadelphia on Thursday, James had been on one of the hottest offensive stretches of his career. He has scored 25 points or more in 18 straight games, the first 17 of those with Anthony Davis out with a left knee injury.
Vogel said James could play in the Lakers' first home game after the team's road trip when they host the Trail Blazers on Wednesday.
"Just going to keep an eye on it day to day," Vogel said.
In his 19th season, James is averaging 29.1 points per game, tied for second in the league, in 36.6 minutes per game, which ranks fourth.
Vogel was asked whether James' knee injury has him thinking about how he will manage the veteran's workload when he returns.
"I think about it every day," Vogel said. "We're always mindful of the load that he's carrying, in constant communication with him and the medical team. And in terms of what we do going forward with the knee and where he's at, it's really a heavy lean on the medical staff and [trainer] Mike Mancias and what they feel is best. It's really not a head-coach thing as much as it is relying on the medical team."
Without James, the Lakers looked great in the early going Sunday. They led Atlanta, one of the league's hottest teams now riding a seven-game win streak, by as many as 11 and scored a season-best 71 points in the first half on 71.4% shooting -- which is the best shooting performance by any NBA team in any half this season. But a 38-20 domination by the Hawks in the fourth quarter, when Trae Young scored 13 of his 36 points, did them in.
"I thought the last two games we played really well, we just fell short," Vogel said afterward. "We always feel like we have enough even [when] Bron -- or in Charlotte, Bron and AD -- are out. We showed we have enough to be right there at the end. We just need to make a couple more plays to get these W's. We could have easily won these last two games, we've just got to make a few more plays."
The Lakers (24-27) are ninth in the Western Conference. They are 5-10 in games without James after Sunday's loss.
L.A. finished its six-game road trip with a 2-4 record, losing the last three games without James.
"We just got to stay the course, man, and I think we got six more games before [the All-Star break]," said Davis. "It will be good for everybody to just kind of get away and then come back and we got to get rolling."