The NFL insists it is conducting a comprehensive investigation of Peyton Manning's alleged use of HGH.

NFL spokesman Brian McCarthy tells the Associated Press that the league launched an investigation “weeks ago,” and that it entails the review of records, interviews, and coordination with other agencies.

It seems to be a direct reaction to the report from ESPN that the NFL declined an invitation to collaborate with Major League Baseball and the U.S. Anti-Doping Agency.

The overriding challenge from the NFL comes from its lack of power to obtain information from anyone other than Manning or any other NFL player, team, or employee.