Los Angeles coach Frank Vogel announced Saturday that James is dealing with a thoracic muscle strain, something ESPN's Brian Windhorst reported is being considered a "significant issue."
James recorded a triple-double (21 points, 12 rebounds and 11 assists) against Milwaukee, but it wasn't enough as the Lakers fell to the Bucks 111-104.
When asked if he was worried about the injury lingering long term, Vogel replied: "We'll see."
Prior to arriving in Los Angeles in the summer of 2018, James had done a remarkable job of being able to make himself available for his team. He never missed more than 13 games in a single season during his first 15 years in the league, averaging 92 games (postseason included) per game from 2003 to 2018.
That average factors in the 2011-12 strike-shortened season, which featured only 66 regular-season games as opposed to the normal 82.
In his first year in L.A., though, James was limited to just 55 games in 2018-19 as he suffered a groin injury on Christmas Day. He subsequently missed 17 games as a result and was later shut down in March as the Lakers fell out of contention.
Load management has become a topic of conversation in Los Angeles, but even in his 17th year, the 34-year-old James has made it clear he intends to play when healthy:
He appeared in all 82 regular-season games as well as 22 postseason games in his final season with the Cleveland Cavaliers in 2017-18.
James has played a major role in the Lakers' early success this season. The four-time NBA MVP is averaging 25.8 points, 10.6 assists and 7.5 rebounds, helping his team to a Western Conference-best 24-5 record.
If the Lakers are going to snap a six-year playoff drought and contend for their first championship since 2010, having a healthy James will be key.