The National Football League (NFL) has opened a comprehensive investigation on claims that football star Peyton Manning uses human growth hormone (HGH). Manning denounces the allegations as "complete garbage".

The NFL started to investigate previous claims regarding Broncos quarterback Peyton Manning's use of HGH. BBC reported that the NFL is currently conducting a comprehensive review which started some weeks earlier. NFL spokesman Brian McCarthy said that they are going through interviews and documents relating to the case.

Manning will be playing at the Super Bowl 50 on February 7 this year. If the HGH claims against Manning are proven to be true, it is possible that the championship match against the Carolina Panthers could be the last game of his career. Use of HGH, a type of performance-enhancing drug, is not allowed by the NFL.

The Washington Post said that the NFL is working closely together with MLB and United States Anti-Doping Agency (USDA) in the inquiry. The two agencies are also investigating similar claims made against baseball players Ryan Howard and Ryan Zimmerman.

The allegations on Manning began in 2011 when an Al Jazeera report claimed that Manning's wife received HGH deliveries. Manning had undergone surgery for his neck injury and was recovering at that time. Charlie Sly, a pharmacist from Texas, said in an unreleased documentary that HGH drugs were being delivered to the Manning household under the name of the wife, Ashley Manning. However, Sly retracted his statements in an ESPN report. He said he only made up the information to test Al Jazeera's undercover reporter.

CBS Sports stated that Manning strongly denied the allegations, describing them as complete garbage. He also defended the medical privacy of his wife and said that he was not using any drugs except those prescribed for him by doctors.

The Denver Broncos backed up Manning's defense, saying that the team gives its 100% support. The Panthers match will be Manning's fourth appearance in the Super Bowl. He has been nominated 5 times as the most valuable player of the NFL.