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American football legend Peyton Manning has denied a claim he was treated with human growth hormone during his recovery from neck surgery in 2011.

The allegation is made in an investigation into doping in sport, which is due to be broadcast on Sunday.

It is claimed Manning was given the banned substance by an Indianapolis clinic, which sent it to his wife.

The Denver Broncos quarterback, 39, said: "The allegation is complete garbage. It never happened."

Manning won the Super Bowl with the Indianapolis Colts in 2006 and is statistically the most successful quarterback in NFL history.

He holds the records for most passing yards and touchdown passes and has been voted the league's most valuable player on a record five occasions.

Manning missed the 2011 season with a neck injury and joined the Broncos in 2012. He is currently sidelined with a foot injury.

"I really can't believe somebody would put something like this on the air," he said. "Whoever said this is making stuff up."

Working under cover, British athlete Liam Collins, who runs in masters events for over 35-year-olds, spoke to Charlie Sly, a Texas-based pharmacist who worked at Indianapolis anti-ageing clinic the Guyer Institute in 2011.

He allegedly names Manning and other high-profile athletes as having received HGH from the clinic.

In a subsequent statement to Al Jazeera, Sly backtracked and said Collins recorded his conversations without his knowledge or consent.

He said: "The statements on any recordings or communications that Al Jazeera plans to air are absolutely false and incorrect.

"Under no circumstances should any of those recordings, statements or communications be aired."