Richards did not take part in the team's morning skate at Staples Center on Thursday, and coach Darryl Sutter said he would not play.
Chicago leads the best-of-7 series, 2-1.
"He didn't skate today, so he won't play tonight," Sutter said.
Richards, who is missing his third straight game with a concussion, skated with the Kings' scratches Wednesday. Sutter did not want to discuss Richards' health when asked for an update on how he felt after skating Wednesday.
"The protocol is very clear," Sutter said. "You've covered enough concussions, surely, you know the protocol."
Richards was injured late in Game 1, when he was hit behind the goal line by Blackhawks center Dave Bolland. Richards has 10 points in 14 Stanley Cup Playoff games.