Any hope of the Dallas Cowboys had that Anthony Spencer might return this season is now gone.
Spencer will have microfracture surgery on his knee and miss the rest of the season.
Cowboys owner Jerry Jones said in his weekly radio appearance Tuesday morning that surgery was likely for Spencer, and Spencer's agent announced it would indeed happen later Tuesday afternoon.,
Jordan Woy, in announcing the surgery on his Twitter account, said he expected Spencer to be healthy by "January or February."
The Cowboys used their franchise tag, with a one-year guaranteed salary of $10.6 million, on Spencer this offseason, and the two sides were unable to agree on a long-term contract and broke off negotiations in June. Spencer, a Pro Bowler last year, will be a free agent after 2013.
He missed the preseason and the season opener after undergoing an arthroscopic procedure on his knee but was able to play in Dallas' Week 2 game against Kansas City, recording two tackles. He was listed as questionable for last week's game against St. Louis but was inactive.
With Spencer unable to return this year, George Selvie is expected to remain the starting defensive end opposite Demarcus Ware. Selvie, signed after the start of training camp, has two sacks this season.
"Here's a case of a guy, you almost have to tie him up to get him off the field," Jones said on his radio show. "He was so diligent in his rehab. The individual that I have the most empathy for is Spencer because of the type of person he is."
Microfracture surgery is a procedure to repair cartilage that provides cushion for bones in knee joints. The recovery time is usually at least four months but can be career-threatening for pro athletes.
Spencer has described his injury as a bone bruise. He had just two days of limited participation in practice before playing 34 snap against the Chiefs. Going into the game, he didn't think he would play more than a dozen or so, but he based that more on conditioning than the status of the knee.
"It didn't seem like it was bothering him at the time," coach Jason Garrett said Monday. "You can't go back eight days ago and say, 'Hey let's have him make 16 plays instead of 30.' We thought we were doing the right thing by him and our football team."
Spencer had the best season of his seven-year career playing under the franchise tag last year. He was the leading tackler and had career highs of 106 tackles and 11 sacks.