PITTSBURGH — Pittsburgh Steelers safety Ryan Clark will sit out Sunday's exhibition game in Denver because playing at a high altitude can trigger a red blood cell condition that caused him to lose his spleen and gall bladder after a 2007 game there.

Clark also didn't play in the Steelers' regular season game in Denver last season. He does plan to run before Sunday night's game to test his reaction to being in the mile-high atmosphere.

Clark became seriously ill after playing in Denver on Oct. 21, 2007, losing more than 20 pounds and missing the rest of the season.