The stress fracture could sideline the Oklahoma star for six weeks, the team announced, promising further information Tuesday.
Griffin, who averaged 13.7 points and 8.1 rebounds per game during the preseason, won't be in the Clippers' lineup when they face the Lakers in their opener Tuesday night, and he could be out much longer. The Clippers play 20 games in their first six weeks of the regular season.
Griffin apparently broke his kneecap during the Clippers' final exhibition game against New Orleans last Friday, perhaps after a dunk that left the power forward wincing in pain. The team initially said Griffin only had a sore left knee, making him questionable for the opener, before revealing the break.
Griffin was the consensus college player of the year with 22.7 points and an NCAA-best 14.4 rebounds per game last season for the Sooners.
After the Clippers won the draft lottery and selected him, Griffin strained his right shoulder during a summer league game in July. The team brought him back cautiously, and Griffin said he was totally healthy in the preseason.
His latest injury is a sadly unsurprising setback for the star-crossed Clippers, who won just 19 games last year in an injury-plagued season. Los Angeles has just two winning seasons in the past 30 years and just one playoff series victory since moving to town in 1984.
Los Angeles was mostly healthy going into this fall, with point guard Baron Davis and center Chris Kaman both ready to play after missing chunks of last season. The Clippers actually have solid frontcourt talent with Marcus Camby, Al Thornton and Rasual Butler alongside Griffin.