Clark didn't play the rest of the 2007 season after becoming ill following an Oct. 21 game in Denver. He was hospitalized overnight in Denver, and his condition worsened after he returned to Pittsburgh.
Clark's spleen and gall bladder eventually were removed, and he lost more than 30 pounds before finally regaining his strength about three months later. Doctors told him his sickle-cell trait was aggravated by the high altitude in Denver and caused a serious blood disorder.
Clark plans to accompany the Steelers to Denver for the Monday night game, but isn't certain if he will be in uniform. He plans to talk to doctors during the Steelers' bye week and again next week, if necessary.
"We'll figure it out. We haven't figured it out yet," Clark said. "We don't know yet."
Clark also had problems playing in Denver while he was with the Redskins in 2005. He was diagnosed then with a bruised spleen, but the severity of his condition wasn't known until he played again in Denver.
Since returning last season, Clark has missed only two games and has not experienced a relapse of his problem, which caused blood vessels to burst and his spleen to become infected before it was removed in mid-November 2007. His gall bladder was taken out a few weeks after that, and his weight dropped from 205 pounds to about 175.
Clark couldn't resume working out and trying to get back into playing condition until January 2008 after the season ended.
Clark said previously he wouldn't play in Denver again unless he was certain there would be no medical problems if he did. He has undergone extensive testing during the last two years, receives six injections a year and treats any infection carefully.
During training camp this summer, Clark joked he might suit up because "there's nothing left they can take out of me" if he goes ahead and plays.
After Clark came back last season, Steelers safety Troy Polamalu said, "It's pretty much a miracle he's out there."
Last year, Clark said the Steelers' medical staff initially questioned not long after that game in Denver why he wasn't playing. It wasn't until he received a second opinion from a different physician that his condition was properly diagnosed and treated.