Oden, the first name announced in the 2007 NBA draft, missed his rookie season because of microfracture surgery on his right knee. The procedure stimulates cartilage growth.

Blazers trainer Jay Jensen said the latest problem with Oden's left knee became apparent about two weeks ago when he experienced some pain and fluid in the joint. Soon thereafter, an MRI revealed the damage.

"We sat there and it was like we'd been kicked in the stomach," Jensen said, choking up. "It felt like hearing someone close to us had died."

Oden was having arguably the best season of his career when he broke his left kneecap during a game last December against the Houston Rockets. He was averaging 11.7 points, 8.8 rebounds and 2.4 blocks as a starter.

The 7-footer often has been compared to former Portland center Sam Bowie, whose career was beset by injuries after the Blazers famously selected him in front of Michael Jordan in the 1984 draft.

The Blazers picked Oden instead of Kevin Durant, who went to the Oklahoma City franchise and has blossomed into one of the NBA's best players.

Another Portland big man, Bill Walton, was selected by the Blazers with the No. 1 pick in the 1974 draft, but he was dogged by a broken nose, foot, wrist and leg over his first two seasons before helping the team to the NBA championship in 1977.

"Some things you just can't explain," Blazers coach Nate McMillan said.

It had been expected that Oden would play this season, but at the start of fall practice he said he wasn't close. When asked at the time if he could return by Christmas, Oden shrugged his shoulders and threw up his hands.

The former Ohio State star has played in only 82 games over parts of two seasons, averaging 9.4 points and 7.3 rebounds.

McMillan said he spoke to Oden on Wednesday.

"As you can expect, the young man is devastated by not having the opportunity to play this season. ... It's like 'Here we go again' for him."

Jensen said Oden has a hole in the articular cartilage on the end of a bone in his knee. It is unclear what caused the damage.

Jensen also said he was as perplexed as anyone as to why Oden was injury-prone. The 22-year-old had MRIs on both knees prior to the 2007 draft, which one onlooker called "pristine," the trainer said.

Asked whether he would be able to come back after the latest blow, Jensen said: "I believe in Greg Oden."