PITTSBURGH -- Steelers' safety Ryan Clark most likely will not play when the team travels to Denver to play the Broncos Monday night, sources said.

Clark has a rare sickle-cell trait that can trigger life-threatening complications at high altitudes. However, doctors have cleared him to play Monday if he chooses to do so.

Clark needed emergency surgery to remove his spleen and gall bladder when he played at Mile High Stadium in 2007 and he lost 30 pounds. Clark also experienced serious complications when playing there with the Redskins in 2005.

Doctors cleared Clark for the game, citing a low risk of him experiencing those same chronic issues again, but Clark told Channel 11 News that complications can’t be ruled out entirely.

"I want to play. It's tough for my wife to see what I'm going through. It's tough to tell the team I'm not gonna play if I've been medically cleared to. But it's up to coach (Mike) Tomlin. We'll make a decision as soon as possible," Clark said.

Clark said a decision about his game status will not officially be made until one hour before game time.

Travis Kirschke strained his calf in the Steelers' win over the Vikings and will likely not play in Denver.

"I think this game might be too close," Kirschke told Channel 11 News.

Running back Willie Parker said he will play Monday, despite leaving practice early Monday with a fever.

"I'm OK. I was just under the weather a little bit," Parker said. "It wasn't the swine flu, but I did have the shivers," he joked.

The Steelers don't think the altitude will have a major impact on the game, but every player Channel 11 News spoke to said they wouldget some extra conditioning in this week with wind sprints and time on the stationary bike.