Lakers head coach Frank Vogel revealed the four-time NBA MVP did the damage during a 105-102 defeat to the Indiana Pacers on Wednesday.
James will be monitored, but the 34-year-old is a doubt for the showdown with the Nuggets at Staples Center, where the Lakers will attempt to stop the rot after back-to-back defeats.
"It was sustained in the Indiana game," Vogel said. "He played through it in the Milwaukee [Bucks] game, but the medical team is just keeping a close eye on him and list him as doubtful [to play on Sunday].