James told reporters he would sit about an hour before the scheduled start of the game. It was the first time the teams have met since Miami defeated San Antonio in Game 7 of the NBA Finals last June.
James said the decision to sit was part of the team's "maintenance" process. Heat teammate Dwyane Wade played Saturday and scored 25 points in 26 minutes, but previously skipped three preseason games.
"No, no injuries -- just not suiting up," James said. "It's OK for LeBron to take one off."
James also plans to miss the Heat's final preseason game Friday at home against the Nets.
Players and coaches from both the Heat and Spurs have talked about the impact the Finals continues to have as they prepare for the upcoming season. The Heat rallied from a 3-2 series deficit by winning the final two games on their home court, including an improbable overtime victory in Game 6 that featured a game-changing 3-pointer from Ray Allen in the final seconds of regulation.
Spurs coach Gregg Popovich said Saturday that he still is haunted by some frustrating memories from the Finals.
"It still goes through my head every day," Popovich said. "The other night, I dreamed about LeBron. Another night, it might be Ray Allen."
James played in each of the Heat's first five preseason games and has gradually rounded into regular-season form after complaining earlier in training camp that his conditioning needed to get better before Miami's Oct. 29 regular-season opener against Chicago.
James has averaged 12.8 points, 4.4 assists and 4.2 rebounds in 24.2 minutes a game in the preseason. He said he plans to be back in the lineup for Wednesday's game against the Pelicans in New Orleans.
The Heat also were without forward Rashard Lewis, who has been away from the team the past week to deal with a family matter.