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In an email to Pro Football Talk, an NFL spokesperson said the NFL is now "reviewing the matter" and that it is procedure to "follow up on any information that potentially involves a violation of this nature."
However, as Florio points out, any formal investigation by the NFL is going to be facing a tough challenge to prove that Manning used HGH. And even if they could prove use, there is a loophole that could have made it OK for Manning to use the banned substance for a short period of time.
Florio, a lawyer, writes:
Beyond interrogating Manning and obtaining information from the Colts regarding Peyton's various treatment regimens while recovering from four neck surgeries, the NFL has no power to force anyone to do anything.
The league lacks the power, for example, to force the Guyer Institute to release records. The NFL can't compel Charles Sly, who was either lying when being secretly recorded or is lying when recanting his story, to cooperate. (More on that later tonight.) The league also can't extract information involuntarily from Ashley Manning.
There's really only one thing the NFL can do: Wait and see whether a criminal investigation results from the allegations.
Florio goes on to point out a bizarre twist in the matter, the 2011 NFL lockout.
According to conversation secretly recorded for Al Jazeera's report, a former intern at an anti-aging clinic said shipments of HGH were sent to Manning's wife in 2011. For four months (March-July) in 2011, the NFL players were locked out by the owners as they worked on a new collective bargaining agreement (CBA).
Without a CBA, there were effectively no rules which means during the lockout, presumably, it would not have been against the rules for players to use HGH.
Of course, at this point, proving when Manning may have used any banned substances is less important than proving or even suspecting that he used them at all. With his career nearly over, and doubts about whether he will even play in 2016, his legacy in the eyes of public opinion is more at risk than his career would be from any potential suspension.