Oden had surgery on his left knee Sunday in Vancouver, Wash., the GM said.
The 7-footer suffered a fractured patella (broken kneecap) in the first period of a 90-89 win Saturday over the Houston Rockets and was carted off the floor at Portland's Rose Garden on a gurney.
Oden, after trying to block a shot by Houston's Aaron Brooks, fell and writhed in obvious pain, clutching the knee for several minutes.
"I'm obviously disappointed having worked so hard to get to where I was," Oden said in a statement released by the team. "This is a setback, but I'll be back. It's in God's hands now."
Oden, a first-round pick by the Trail Blazers in the 2007 NBA draft out of Ohio State, missed the 2007-08 season after microfracture surgery on his right knee. He also missed chunks of last season with a foot injury and a fractured left kneecap. In 2006, he had surgery on his right wrist.