Steelers coach Mike Tomlin made the same decision last January when he chose to sit Clark, who carries the sickle cell trait, in Denver for what turned out to be a season-ending playoff loss for Pittsburgh.
"That has been our position in the past and will continue to be our position," Tomlin on Tuesday said of Clark not playing. "Ryan understands that and is supportive of that. I am sure he will be a big supporter of his teammates, not only in the stadium this week but in preparation. He always has been that guy and I expect that to continue."
Sickle cell trait is a genetic abnormality which can affect red blood cells. Clark was playing in Denver in October 2007 when he developed significant pain in his left side. He became gravely ill and ultimately lost his spleen and gall bladder, along with the remainder of that football season, as a result.
While Clark was eventually able to regain his health and return to football, the possibility of another episode in high altitude was not something the Steelers wanted to risk.
Clark will travel with the team and be on the sideline Sunday night. He will not dress for the game.
Clark is also offering his support to increasing awareness and improving treatment for sickle cell. On Tuesday, he will introduce Ryan Clark's Cure League in partnership with University of Pittsburgh Medical Center (UPMC), the University of Pittsburgh's Vascular Medicine Institute and the Institute for Transfusion Medicine, where former Pitt and Chicago Bears alumnus Jim Covert is CEO. The initiative aims to raise awareness, donations and support that will lead to better care and, ultimately, find a cure for this inherited blood disorder.
Clark lost a sister-in-law shortly afterward to the same condition, and one of his children also carries the sickle cell trait. Those who carry it are typically free of symptoms, but as Clark discovered, when under extreme circumstances such as dehydration or high elevation, the condition can result in severe pain or, in the worst cases, death.
Clark's personal history with the sickle cell gene and disease inspired him to establish the foundation which will bear his name. Ryan Clark's Cure League formally launches its website -- www.CureLeague.org -- on Tuesday.
"We're going to dedicate our efforts solely to sickle cell research and patient care," Clark said. "What we're hoping is we can be the pioneers here."
An estimated 2 million Americans carry one of the sickle cell genes.