Tevin Coleman and Devonta Freeman have combined to make up the most dynamic backfield in the NFL through four weeks of the 2016 season.
Could the Atlanta Falcons be without one of those key cogs when they travel to Denver to face the undefeated Super Bowl champion Broncos?
"With my sickle cell, I have no idea if I'll play there,'' Coleman told ESPN.com's Vaughn McClure. "I really don't know how I'll feel or how it will be like. I've never been to Denver.''
Coleman carries the sickle cell trait, a genetic abnormality affecting red blood cells, which is worsened at high altitudes, such as Denver, sometimes causing severe dehydration or trouble breathing.
Famously, former NFL corner Ryan Clark, who has the trait, became gravely ill in 2007 while playing for the the Pittsburgh Steelers in Denver. Clark had his spleen and gallbladder removed. Clark missed two subsequent games in Denver, including the Steelers' 2011 playoff loss to Tim Tebow's Broncos.
"It does make me scared a little bit, a little nervous, because I'm risking my life,'' Coleman said, referring to Clark's experience. "We'll have to see. I'll have to talk to coach (Dan Quinn). I guess coach will see how I feel when we get there. And I just have to communicate with him, if I am out there (playing), if I'm dead (tired) or can't breathe. We just have to play it smart.''
Last season, Bengals defensive tackle Geno Atkins played in Denver with the sickle cell trait. Atkins played 39 of 65 defensive snaps (60 percent). The Bengal's went into the game planning to monitor Atkins.
Falcons head coach Dan Quinn said on Monday that he expects Coleman to play Sunday.
The running back said he plans to do more research ahead of the trip because he's never played in high altitudes.
"(Not playing) would bother me quite a bit,'' he said "I'd be real upset because my team is going to be out there, and I want to compete and battle for my team. Watching them play, you just want to be out there and ball with them. I'd be really disappointed if I can't play, but I'd understand because things could happen.''
Even if Coleman plays, the Falcons could take it easy on him and ride Freeman for one game.