Clippers assistant coach Tony Brown will fill in for Dunleavy on the sideline.
Dunleavy appears to have aggravated the injury by sneezing.
"He's been sick the last couple of days and believe it or not, I think this came about because he sneezed really violently," assistant general manager Neil Olshey said. "As soon as he sneezed, he totally threw his back out. He had to crawl over to the bed and get his Blackberry so he could get in touch with our trainer.
"I'm not even sure he's up off the floor yet, so he couldn't coach the game tonight. Anyone who has ever had a back injury like this can relate to how bad it can be."
Asked about the bizarre nature of the injury and its possible link to the team's history of bizarre and unfortunate injuries, Olshey laughed. "Well hopefully this means we can leave this all behind in 2009. I think Mike just took this one for the team, because now it's just the coach getting hurt and not a player."
Sixers forward Elton Brand, playing in his first game at Staples Center after leaving the Clippers in a messy free agent signing in the summer of 2008 seemed surprised that Dunleavy would not be in the building for his return.
"Did coach throw out his back shooting those threes in practice?" Brand asked with a smile. "We'll miss our [hug] on the sidelines."
Dave McMenamin and Ramona Shelburne are writers for ESPNLosAngeles.com