The US National Football League (NFL) says it is has launched a "comprehensive" investigation into the findings of an Al Jazeera documentary on sports doping in professional sports.

The Al Jazeera investigation, broadcast last month, included the claims of a pharmacist who previously interned at an anti-ageing clinic in Indiana. He told an undercover reporter that the clinic shipped human growth hormone to the wife of star NFL quarterback Peyton Manning.

On Tuesday, the NFL released a statement to US media, saying that its review of the claims are "ongoing and comprehensive".

New evidence emerges in Al Jazeera doping probe

"It involves obtaining and reviewing numerous records, conducting multiple interviews and working with other entities," the statement said.

"We do not comment on the specifics of these matters until the review is completed."

The statement added that the league was working with Major League Baseball (MLB) and the US Anti-Doping Agency (USADA).

It was released after an ESPN report said that the MLB had asked USADA to help investigate claims made about a number of players named in the Al Jazeera investigation.

The ESPN report, citing lawyers familiar with the baseball investigation, said the NFL declined to coordinate its investigation with the MLB and USADA.

Manning has denied using performance-enhancing drugs and says he will assist NFL investigators.

The 39-year-old five-time Most Valuable Player is set to play for the Denver Broncos in the championship Super Bowl game on February 7 against the Carolina Panthers.

Source: Al Jazeera