Denver Broncos quarterback Peyton Manning is welcoming the NFL investigation into his alleged use of human growth hormone (HGH).

Manning came under fire after an Al Jazeera report said his wife, Ashley, received HGH from a clinic in Indianapolis, where the family lived at the time.

The source of the report, a pharmacist at the institute, since recanted his story and Manning has called the report "a joke" and "garbage" multiple times since it surfaced in December.

Preparing for Super Bowl 50, which sees the Broncos take on the Carolina Panthers, Manning said he was glad to see the NFL investigating.

"I welcome this NFL investigation. I know the rules of the NFL and I respect the rules and they're important to me," the 39-year-old said.

"What this report alleges that I did is simply not true. It's fabricated. It's junk. It's garbage.

"I could give you a long list of other words for it and I can guarantee you this investigation, what it'll find is absolutely a big fat nothing.

"That's how I feel about it."

Manning may yet retire following Sunday's Super Bowl, but he refused to be drawn on talk surrounding his future.