James was injured during the Lakers' 127-101 victory over two-time defending NBA champion Golden State on Christmas when he slipped while going for a loose ball.
An MRI revealed that James sidestepped serious injury, but he did suffer a significant left groin strain and the Lakers are preparing for him to miss several games, league sources told ESPN's Brian Windhorst and Adrian Wojnarowski. The Lakers are calling James' absence "day to day," but sources tell ESPN that there is a healing process that needs to occur before James can return to the lineup.
"It's one of those things we want to make sure he's healthy before we get him back out there," coach Luke Walton said Thursday. "That could be an injury where if you come back too early you re-injure it and then you're out longer. We'll be careful and cautious when he starts playing again."
The Lakers looked just fine for 3½ quarters in their first game without James, but it was a different story down the stretch, when the four-time MVP's absence was noticeable and costly.
Los Angeles led 104-89 with 6:44 left following a dunk by Tyson Chandler, before Sacramento surged back. Bogdan Bogdanovic, who had 11 points through three quarters, sparked the comeback with 12 points in the fourth, including the winning 3-pointer at the buzzer.
"This is the first close game we've been in that he's not there," Walton said. "If LeBron James is playing in that game it probably finishes a little differently. When you get the best closer in the game on your team, then you rely on him to do that. All that said, we made enough plays to win."
James, who remained in Los Angeles while his teammates flew to Sacramento, had previously played in every game since the finale of the 2016-17 regular season, when he sat out to rest. His last extended absence because of injury was an eight-game stint to deal with back and knee aches midway through the 2014-15 season.
James, who turns 34 on Sunday, is averaging 27.3 points, 8.3 rebounds and 7.1 assists this season, his 16th in the NBA and first with the Lakers.
The Associated Press contributed to this report.