Eli Manning’s smoking-gun ­e-mail allegedly seeking phony game-worn gear meant to dupe collectors was sent too long ago for the FBI or New Jersey state prosecutors to bring criminal fraud charges, sources said Friday.

The federal statute of limitations is five years — and it is six in the Garden State — and the e-mail from Manning to an equipment manager asking for “2 helmets that can pass as game used” was sent in 2010.

But that doesn’t mean the ­Giants star is in the clear.

Legal experts say the e-mail and another sent by the Giants star about the equipment could be still be used against him if evidence of a fraud within the last five years emerges.

“A conspiracy is chargeable even if some of the conduct occurs more than five years ago so long as you have an overt act in furtherance of the conspiracy that happened within five years,” explained Robert Ray, a former prosecutor and attorney with Thompson & Knight.

Manning, who has a contract with memorabilia dealer Steiner Sports, has been accused in court documents filed by three collectors of defrauding them by passing off bogus equipment as authentic, game-worn gear.

The collectors are pressing a civil racketeering suit against the Giants, Manning, Giants equipment manager Joe Skiba Steiner and others.

The plaintiffs claim Manning continued to pass off fake gear as the real deal as recently as May 2012 — but they don’t offer any hard evidence in the court papers.

Investigators with the US Postal Service opened a probe into the Giants memorabilia scandal with the help of federal prosecutors — but it’s not clear if that investigation is still ­under way, sources said.

As recently as October, federal agents interviewed Skiba “in connection with . . . memorabilia fraud,” court papers say.

Skiba said he was “questioned by agents upon arriving at Newark Airport after the team’s 2016 regular-season game in London.”

In a document filed earlier this month, the Giants’ lawyers also confirmed they had been in contact with the Manhattan US Attorney’s Office, which opened a probe in 2014, right after the civil racketeering lawsuit was filed.

Manning declined to comment when approached by The Post outside the Somerset Hills Country Club on Friday. “No, not at the moment. Thank you, though,” he said.

His former teammate, Brandon Jacobs, defended the quarterback.

“Eli was not involved in none of that,’’ he told The Post. “That’s one of the most wholesome guys I’ve ever been around in my life.”

Additional reporting by ­Danika Fears