Peyton Manning was supplied with human growth hormone in 2011 from an Indianapolis anti-aging clinic, according to Huffington Post and other media outlets, and details will come out in a documentary from Al Jazeera scheduled to air Sunday night.

Manning and other athletes are named in the report in which Liam Collins, a British hurdler, went undercover in an attempt to expose the widespread nature of performance-enhancing drugs in global sports, according to the Huffington Post.

“The allegation I would do something like that is complete garbage and is totally made up,” Manning said in a statement. “It never happened. Never.”

As part of the investigation, Collins connected with Charlie Sly, a pharmacist based in Austin, Texas, who worked at the Guyer Institute, the Indiana-based anti-aging clinic, in 2011.

Manning missed the 2011 season, when he was a member of the Indianapolis Colts, after undergoing neck surgery. In the documentary, Sly tells Collins – who is taking secret video of his interactions – that he was “part of a medical team that helped (Manning) recover” from the surgery. Sly also claims that the clinic mailed growth hormone and other drugs to Manning’s wife, Ashley Manning, so that the quarterback’s name was never attached to them.

“All the time we would be sending Ashley Manning drugs,” 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.”

Manning and his wife also came to the clinic after its normal business hours for intravenous treatments, Sly tells Collins on the undercover video.

Manning left the Colts after the 2011 season to sign with Denver. The NFL banned human growth hormone as part of its 2011 collective bargaining agreement with players, but did not begin testing for it until 2014. No player has ever tested positive.

The credibility of the report hinges largely on the credibility of Sly. Several details lend significant credibility to Sly’s assertions. First, Sly and the ring he is associated with do, in fact, obtain drugs for Collins, which the network says it retained as evidence.

In another stunning scene, Taylor Teagarden, an eight-year MLB veteran, appears in one of the undercover videos, openly discussing his use of performance-enhancing drugs during the previous season.

Al Jazeera confirmed that Sly did work at the anti-aging clinic that treated Manning.

Beyond the allegations against Manning, the report calls into question the effectiveness of testing regimes meant to prevent performance-enhancing drug use in professional sports, from American leagues to the Olympics.

“The Dark Side” paints a picture of an underground marketplace where athletes can easily obtain drugs that are hard to detect even with sophisticated drug tests like those implemented by MLB, the NFL and the Olympics. And it raises questions about how serious the owners of professional sports teams are about rooting out drug use, which can make the games more exciting and profitable, while doing damage to the bodies of players, not owners.

“No one’s got caught, because the system’s so easy to beat,” pharmacist Chad Robertson brags to Collins. “And it still is, that’s the sad fact. I can take a guy with average genetics and make him a world champion.”

According to the Huffington Post, Robertson designed a program for Collins that included prescription fertility and hormone drugs, other substances labeled as “not for human consumption” and illegal drugs. Sly, meanwhile, preached the effectiveness of Delta-2, a hormone supplement that is “steroidal in nature” but is not an anabolic steroid, according to online product descriptions.

“There’s a bunch of football players who take this, and a bunch of baseball players who take it too,” Sly tells Collins in the documentary.

MLB has banned the drug explicitly.

The report, according to the Huffington Post, does not link Manning to Delta-2, but Sly and Robertson name multiple football players as customers, including Green Bay Packers linebacker Mike Neal. Neal, Sly says, connected him with multiple teammates, including defensive end Julius Peppers. Pittsburgh Steelers linebacker James Harrison is another NFL player he has supplied, Sly says.

Sly also names Philadelphia Phillies first baseman Ryan Howard and Washington Nationals infielder Ryan Zimmerman as players who received the drug from him. He also claims in the report he gave drugs to Mike Tyson.

“We just used Delta-2 because it wasn’t detectable,” Sly says.

According to the Huffington Post, Sly also says that he provided Clay Matthews, Green Bay’s Pro Bowl linebacker, with the prescription painkiller Percocet to help him deal with pain before at least one game. He also brags in one undercover video that Matthews texted him in an attempt to obtain Toradol, a powerful painkiller that is banned in many countries but not in the United States.

Harrison, Zimmerman and Howard all denied using the drugs to the network. Neal, Peppers, Matthews and Tyson did not respond to Al Jazeera’s request for comment.

Robertson, the pharmacist, and Spletzer, the neuropathic physician, did not respond to Al Jazeera’s request for comment. Sly, when pressed by Al Jazeera, backtracked, saying that his claims about supplying the drugs to athletes were “false and incorrect.”

In a subsequent statement to Al Jazeera, he walked back the comments even further, saying that Collins took advantage of him while Sly was grieving the death of his fiancee.