Peyton Manning's legendary career with the Denver Broncos is suddenly, stunningly, a topic for debate after an Al Jazeera report linked him to human-growth hormone. Manning is one of the greatest players in NFL history, and he is now under the microscope for alleged cheating. But Manning has two crucial factors working for him as this story develops: the sterling reputation he has built and the less-than-sterling reputation of his sport.

The undercover report, which broke Saturday evening, is certainly a bombshell: a pharmacist who worked at an anti-aging clinic in Indianapolis claimed to have supplied Manning's wife, Ashley, with HGH in 2011, the year Manning took off from football to recover from a neck injury before starting his comeback the following season with Denver.

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"All the time we would be sending Ashley Manning drugs," pharmacist Charlie Sly says in the video. "Like growth hormone, all the time, everywhere, Florida. And it would never be under Peyton's name, it would always be under her name." Sly also said Manning came to the clinic afterhours for IV treatments. HGH has been banned by the NFL since that same year, 2011.

Through the Broncos, Manning released a statement late on Saturday: "The allegation that I would do something like that is complete garbage and is totally made up. It never happened. Never. I really can't believe somebody would put something like this on the air. Whoever said this is making stuff up."

The report, scheduled to broadcast in its entirety on Sunday, does not rely on the kind of documentation that would paint Manning into a corner, as far as we know at the time of this writing. Mailing slips or phone records would be a lot more troubling than the recorded words of one pharmacist in Indiana. This could be someone who is fibbing to convince a potential client of his importance, and medical "experts" have done exactly that through fabrication. And in a short video appended to the report, Sly himself says his own statements in the Al Jazeera report are "false and incorrect."

Still, the timing here is curious: Manning's career in Denver is considered miraculous, as his numbers after multiple neck surgeries are good enough to put him in Canton even without his Hall of Fame career in Indianapolis. In 2011, Manning said in a statement, "I simply am not healthy enough to play, and I am doing everything I can to get my health back." Those were desperate times for an aging star, and they led to triumphant times. We've seen that movie before in sports.

If Manning used HGH, it would threaten to tarnish his MVP season and the Broncos' AFC title in the 2013 season – the season in which Manning threw 55 touchdowns.

Yet right now, we have a very popular athlete who got that way through many years of hard work and accessibility. He is not only beloved for two careers before 2011 – at Tennessee and in Indianapolis – but also for his folksy affability and his charity work. Faith in him will not crumble easily and it may not crumble no matter what this reveals.

That's in part because of the sport Manning plays. This is not Major League Baseball, where legends like Barry Bonds and Roger Clemens turned into pariahs. It's not track, where sprinters can't break a single record without millions of raised eyebrows. This is football, where there is a tacit understanding among fans that the brutality of the sport makes it impossible to maintain health over the long term. Manning's history of injuries and surgeries made him especially vulnerable to every hit. This is no excuse for any performance-enhancing drug use, but in football the blame is quicker to fall on the sport than it is on the athlete. The NFL, after all, is not known for looking out for the health and welfare of its players.

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