DENVER | An Al Jazeera America investigation saying that Peyton Manning used illegal performance-enhancing drugs came under attack Sunday after the report’s source recanted his allegations.

Charlie Sly, the source behind the Manning allegation cited in the investigative report, “The Dark Side,” posted a video late Saturday saying that he had been videotaped without his knowledge or consent by Al Jazeera’s Liam Collins, a former British hurdler.

“The statements on any recordings or any communications that Al-Jazeera plans to air are absolutely false and incorrect,” Mr. Sly said on YouTube. “To be clear, I am recanting any such statements and there is no truth to any statement of mine that Al Jazeera plans to air. Under no circumstances should any of those statements recordings or communications be aired.”

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“The Dark Side,” which has been posted on YouTube, is scheduled to air Sunday night on Al Jazeera America. The report is billed as a six-month undercover investigation into “the secret world of doping.”

In a statement, Mr. Manning described the report as “complete garbage” and “totally made up.”

He has since hired former Bush White House spokesman Ari Fleischer, who runs a sports-communications company, who called the report “junk journalism,” according to the Denver Post.

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Al Jazeera did not respond immediately Sunday to a request for comment, but did include in a website post Sunday both Mr. Sly’s disavowal and Mr. Manning’s denial.

Mr. Sly told ESPN’s Chris Mortenson that he was purposely dropping famous names and giving false information to Mr. Collins in order to “determine whether this guy was legitimate or just trying to steal some knowledge about the business.”

Mr. Sly said he was a pharmacy intern in 2013 at the Guyer Institute in Indianapolis, where Mr. Manning received treatment for an injury in 2011. The Al Jazeera report identifies Mr. Sly as a pharmacist.

“When I was there, I had never seen the Mannings ever. They were not even living there at that time,” Mr. Sly said. “Someone who worked there said they had been there before. That was the extent of any knowledge I had. I feel badly. I never saw any files. This is just amazing that it reached this point.”

The Al Jazeera report alleges that the Denver Broncos quarterback received shipments of human-growth hormone [HGH] mailed to his wife, Ashley Manning.

The Denver Broncos quarterback told ESPN that he had received legal therapy under Dr. Guyer, including nutrition and oxygen therapy, “but never HGH,” adding that, “My wife has never provided any medication for me to take.”

Both the Denver Broncos and Mr. Manning’s former team, the Indianapolis Colts, issued statements Sunday in support of the quarterback.

“Knowing Peyton Manning and everything he stands for, the Denver Broncos support him 100 percent,” the team said. “These are false claims made to Al Jazeera, and we don’t believe the report.”

The statement continued that, “Peyton is rightfully outraged by the allegations, which he emphatically denied to our organization and which have been publicly renounced by the source who initially provided them.”

The Indianapolis Colts, where Mr. Manning played for 14 years, issued a statement calling the Al Jazeera allegations “utterly ridiculous.”

“Peyton played the game in Indianapolis for 14 years the right way. He never took any shortcuts and it would be absurd to suggest he would have taken prohibited performance-enhancing drugs,” said the Colts. “We also note that the ‘source’ of this allegation has since recanted his story. The entire Indianapolis Colts organization and the Irsay family hope this crude effort to besmirch Peyton’s reputation will not be permitted to tarnish the legacy of a great Colt.”

In the undercover interview, Mr. Sly also mentions Washington Nationals infielder Ryan Zimmerman, Philadelphia Phillies slugger Ryan Howard, and ex-boxer Mike Tyson.

“When I realized Al Jazeera was using a secret taping and Collins as a so-called investigative reporter, I was baffled,” Mr. Sly told ESPN. “I cannot believe that can happen. That’s why I recanted the story. It wasn’t true, and I was trying to pull one over on Collins to see if he had any idea of what he was talking about.”