The NFL says it is conducting a comprehensive review of allegations that Broncos quarterback Peyton Manning had human growth hormone delivered to his house.
There's no timetable to complete the investigation, but it's not expected before Denver play Carolina in the Super Bowl on February 7.
League spokesman Brian McCarthy says the inquiry, which began weeks ago, involves reviews of records, interviews and coordination with other agencies.
Al Jazeera reported last month an intern at an Indianapolis anti-aging clinic was secretly recorded suggesting Manning's wife had received deliveries of HGH, which is banned by the league.
Manning, then with the Colts, was rehabilitating from shoulder surgeries.
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The intern, Charles Sly, has since recanted his story.
Manning angrily denied using performance-enhancing substances and called the report "complete garbage".
