Mathias Kiwanuka out indefinitely

EAST RUTHERFORD, N.J. -- In a devastating blow to the Giants' defense, linebacker/defensive end Mathias Kiwanuka is out indefinitely after tests revealed a bulging cervical disc in his neck.

The injury came as a surprise because Kiwanuka participated fully in practice all week.

A team official said Kiwanuka initially complained of stiffness in his neck Thursday morning and was treated by Ronnie Barnes, the team's vice president of medical services. He practiced Thursday and underwent an MRI on Thursday night. Kiwanuka then practiced again Friday, and intentionally avoided contact with his head and neck during the morning session.

After Friday's practice, Kiwanuka went to the Hospital for Special Surgery for a CAT scan and was examined by Dr. Russell Warren. The doctor consulted with a spine specialist at the hospital and diagnosed Kiwanuka with the bulging disc.

It's unclear when Kiwanuka initially suffered the injury, but sources told ESPN.com senior NFL analyst Chris Mortensen that the tests were alarming enough that the Giants are bracing for a worst-case scenario of Kiwanuka missing two to three months and perhaps the rest of the season. However, as both sides seek different opinions, there also remains the best-case scenario that treatment, possibly through injection to calm down the disc, could allow for a return to action at some point, a source told Mortensen.

Team physicians will monitor Kiwanuka, and have advised him to avoid contact with his head and neck.

"It's disappointing," Kiwanuka said in a statement released by the team. "It just feels like a stiff neck. The pain is not intolerable but I want to make sure that I will be okay down the line."

Kiwanuka's injury brings to mind the neck ailment former Giants linebacker Antonio Pierce suffered in 2009.

Pierce injured his neck Oct. 25 against the Cardinals and eventually was diagnosed with a bulging disc in his neck. Pierce initially was optimistic about returning to the field. But after seeking two medical opinions, the Giants opted to shut to Pierce down for the remainder of the season. Pierce said he would have needed surgery to keep playing and opted to retire after the season.

The team initially hoped Pierce's injury would heal with treatment and time away from the field. It seems the Giants are taking the same approach with Kiwanuka, whom they took in the first round of the 2006 draft.

Giants coach Tom Coughlin spoke about Kiwanuka's versatility Friday and said the team will have to regroup without the fifth-year player. Coughlin also acknowledged the difficulty of adjusting to life without Kiwanuka so late in the week.

"Obviously, Kiwi is a big part of our plans. He's had a very good season. He's very flexible. He's a versatile athlete who can be used in a lot of different ways," Coughlin said. "So now we have to regroup and try to figure out how we're going to utilize our personnel for this game."

Osi Umenyiora is questionable for the Bears game after he sat out of Friday's practice with swelling in his right knee, but Coughlin said he expects Umenyiora to play. However, linebacker Keith Bulluck is listed as doubtful with turf toe.

If both Kiwanuka and Umenyiora can't play Sunday, the Giants might turn to rookie defensive end Jason Pierre-Paul and reserve defensive end Dave Tollefson.

They also have the option of moving defensive tackle Chris Canty to defensive end and playing rookie defensive tackle Linval Joseph. Joseph has been inactive for the first three weeks of the season.

Kiwanuka, whose 2007 season was cut short when he broke his leg in Week 10, is in his contract year and hinted last week that he was looking forward to testing the free-agent market. He has four sacks and 11 tackles in four games this season.

"For me, it's the last year of my contract. It's a good opportunity for me to showcase the skills that I have," Kiwanuka said last Friday. "So whatever this team asks me to do, I'll do it, and next year will be a new year."

Kiwanuka has proved particularly valuable to Giants first-year coordinator Perry Fewell, who has used the 27-year-old at linebacker, defensive end and defensive tackle this season.

Kiwanuka said he would cooperate fully with the team's medical staff and seems eager to return to the field.

"I have full trust in the medical staff and the trainers at the Giants," Kiwanuka said in a statement released by the team. "I'm going to do everything that is asked of me so when I'm cleared I'll be back and ready to go."

Ian Begley is a regular contributor to ESPNNewYork.com.