The Portland Trail Blazers have announced that center Greg Oden underwent microfracture surgery on his left knee. The surgery was performed by Dr. Richard Steadman in Vail, Colo. Oden will miss the remainder of the 2011-12 NBA season.

"Initially, Greg was undergoing a procedure similar to the one he had a couple of weeks ago to have debris cleared from his right knee," said Acting General Manager Chad Buchanan . "However, once the doctors were inside Greg's left knee, they unfortunately found articular surface damage and determined microfracture was necessary."

Oden will become an unrestricted free agent at the end of this season.

"This is not the news we were hoping for Greg or the organization," said Trail Blazers President Larry Miller. "It's hard to put into words the heartbreak for everyone involved, but especially for Greg. He's a young man who has experienced a great number of physical challenges in his playing career and today is yet another significant setback for him. We have a lot of empathy for Greg and his family during this difficult time."