Jeff Green starts in his place for Boston as the already size-deprived Celtics get even smaller.
"We just decided to be the mini Celtics," quipped Rivers.
Rivers has been hinting that he'd like to rest Garnett in upcoming games and, after the 36-year-old looked gassed at times against the Lakers on Wednesday, Rivers realized he may have waited too long.
"I was telling our coaches after the Denver game, it's sacrilegious not to play KG against the Lakers, but it was a thought," said Rivers. "And watching him play, you’re sitting there kicking yourself thinking, ‘That should have been the night for him,’ because it was a back-to-back. It is what it is."
Garnett, who participated in the team's morning shootaround but politely declined to talk with the media, didn't put up a fight about sitting out. He's expected to be back on the floor when the Celtics visit Portland on Sunday night.
"He was fine with it, which told me that it was the right thing," said Rivers. "He didn’t put up a fight at all, that tells you we were probably a game or two too late. We should have done it a game earlier."
Rivers said the team will consider resting Garnett again later in the season with the goal of preserving all the players on an already injury-thinned roster. Boston is particularly thin on big men, having dealt away veteran Jason Collins at Thursday's deadline in order to acquire guard Jordan Crawford from the Wizards.
Rivers confirmed Boston is set to sign 26-year-old forward D.J. White, who just wrapped a season in China. He could join the team on a 10-day deal as early as Sunday.
"Listen, it’s all visual, with all these guys," said Rivers. "Kevin, we knew at some point we were going to sit him. And we'll probably sit him at least one maybe two more times before the playoffs. Everyone else, we just go visual."
The Celtics have lost two straight coming out of the All-Star break to start a five-game road trip. Boston entered Friday's action sitting as the seventh seed in the Eastern Conference, 1½ games ahead of the Milwaukee Bucks.