James injured his right groin in the second quarter Friday night in a 108-103 overtime loss at Sacramento that snapped Miami's six-game winning streak. He stayed in the game and finished with 33 points, eight rebounds and eight assists.
James, selected The Associated Press Male Athlete of the Year this week, also tweaked his left ankle in the loss.
The four-time NBA MVP warmed up before the game against the Trail Blazers, but was declared inactive about an hour before the tipoff. He was replaced in the starting lineup by Michael Beasley.
James leads the Heat with an average of 25.2 points, 6.9 rebounds and 6.5 assists.
James was not available for comment before the game, but he did address the injury following the loss at Sacramento, saying: "It doesn't feel good right now."
The two-time defending champions also were without Chris Andersen (sore back), but Ray Allen (right knee tendinitis) and Dwyane Wade (rest), who both missed the game against the Kings, were in the lineup.
James was the only Miami player to start the team's first 29 games.
"No excuses for us," Wade said. "This is the NBA. Injuries happen. Guys have to step up."
During the Sacramento loss, James passed Larry Bird (21,791 points) and Gary Payton (21,813 points) to move into 29th place on the NBA's career scoring list.
With 21,819 career points, the next player in front of James is Clyde Drexler at 22,195.
James has given the Blazers trouble at the newly renamed Moda Center. In 10 ges in Portland, he has averaged 29.6 points, 9.9 rebounds and 7.2 assists.
He is listed as day-to-day. He turns 29 on Monday when the Heat play at Denver to wrap up a four-game trip.