The Lakers revealed Saturday that James was dealing with a thoracic muscle strain -- a pull in the rib cage area -- that he suffered earlier in the week against the Indiana Pacers and then played through against the Milwaukee Bucks on Thursday. James is also dealing with a nagging groin issue, sources told ESPN's Brian Windhorst.
James, who turns 35 this month, is averaging 25.8 points, 7.5 rebounds and a career-high 10.6 assists while playing a career-low 34.8 minutes.
Although James was out, Kyle Kuzma, who had missed the previous five games with a left ankle sprain, returned to the lineup on Sunday with a minutes restriction. He scored 16 points in 22 minutes.
"We're a next-man-up team, but this is not one guy that's got to step up and fill [James'] shoes," Lakers coach Frank Vogel said. "It's got to be a team effort. Everybody has got to be aggressive. We have to make sure the ball is moving side to side."
Sunday marked three days of rest for James. The Lakers' schedule allows for James to get two more rest days before a determination will have to be made about his playing status for Wednesday's Christmas showdown against the LA Clippers.
"We'll see," Vogel said of James' recovery. "The medical team is just telling me he's day-to-day. ... We'll take it one day at a time."