James first sustained the injury, a pull in the rib cage area, against the Indiana Pacers on Tuesday and played through it during Thursday's loss to the Milwaukee Bucks. James didn't require an MRI, but this is a significant issue and not just a load management situation, sources told ESPN.
Earlier this week, James said he didn't plan to miss any games this season for rest. James has also been dealing with a nagging groin issue recently, sources said. Last season a groin strain on Christmas Day derailed James and the Lakers' season.
Although he has yet to miss a game, the Lakers have been managing James' minutes this season as he's averaging a career-low 34.8 per game. Despite the injury, James played 37 minutes and registered his seventh triple-double of the season against Milwaukee, but he struggled at times in the loss. The Lakers were outscored by 14 points when he was on the floor.
"If [James] doesn't go [Sunday] then we'll need a group effort," Vogel said Saturday. "We'll release starting lineups and all that stuff tomorrow but it's one of those things that no one person can pick up everything that LeBron does for our team, so just have to be a group effort."
Meanwhile Lakers forward Kyle Kuzma, who has been dealing with a sprained left ankle, practiced on Saturday and is probable to play against the Nuggets. Kuzma hasn't played since Dec. 8 and has been limited to just 20 games this season.
The Lakers are looking to bounce back from losing back-to-back games for the first time all season against Denver, which enters Sunday's game having won five straight games.