The Steelers placed the 35-year-old Smith on injured reserve on Saturday. He hasn't played since injuring his foot Oct. 2 against Houston and the neck problem was discovered by doctors while he was out with that injury.
"He was experiencing some (neck) discomfort and pain," coach Mike Tomlin told the Pittsburgh Post-Gazette on Sunday. "He thought it was a function of playing. Once he hurt his ankle, he thought it would calm down but it didn't. He consulted with our doctors and let them know what he was experiencing. They evaluated it and looked at it and determined that it needs to be fixed."
This marks the third straight season that injuries have limited Smith. He played in only 11 games spanning the 2009 and 2010 seasons due to shoulder and triceps injuries and appeared in just four this season.
"Just disappointed, that's about it," Smith, who accompanied the team to Arizona for Sunday's 32-20 victory over the Cardinals, told the Post-Gazette when asked about his neck. "You work hard, circumstances change and it doesn't work out."
The move probably signals the end of his career because the Steelers already have Smith's replacement in 2009 first-round draft pick Ziggy Hood, who has excelled in Smith's absence.
Smith, a 1999 fourth-round draft pick by the Steelers out of Northern Colorado, was possibly the most unheralded figure on the Steelers defenses. From 2000 to 2008, when Smith had double-digit starts, Pittsburgh ranked in the top 10 in defense all nine years including four as the top-ranked unit. During his career, Smith had at least four sacks in six seasons and is 10th on the team's all-time list with 44.
Brett Keisel was among the members of the Steelers defense who said they planned to dedicate the 2011 season to Smith.
"He's one of the greatest Steelers to ever put on a uniform," Keisel told the Pittsburgh Tribune-Review. "There aren't a lot of guys who have played and battled like he has. Everyone looks up to that. We love him. We respect him. The least we can do is go out and win games for him."
Information from ESPN.com NFC North blogger Jamison Hensley was used in this report.