If you thought the Al Jazeera investigation into athlete doping had gone away now that Peyton Manning has strolled into the sunset with another Super Bowl title, think again.

It's back with a vengeance, just as the 2016 season is set to begin. And it could impact the NFC North race.

The initial report came out in late December, with undercover work attempting to expose performance-enhancing drug use by several prominent athletes, many of them in the NFL.

Manning made most of the headlines at the time. But the NFL said last month it has closed its investigation of the now-retired QB, adding he fully cooperated with the proceedings. Four other players? Not so much, according to USA Today and other publications that Monday obtained a letter sent by the league to the NFLPA.

Two of them, the Packers' Clay Matthews and Julius Peppers, are key defensive players for the Vikings' chief NFC North rival this season. Steelers linebacker James Harrison and free agent Mike Neal, who was with the Packers last season, are the other two named in the letter, which doesn't mince words.

The upshot: the players are said to have not cooperated with the investigation, and if they don't submit to an interview on the matter by Aug. 25, they will be suspended indefinitely.

Yeah, you read that right.

Per the league: "The suspension for each such player will begin on Friday, August 26 and will continue until he has fully participated in an interview with league investigators, after which the Commissioner will determine whether and when the suspension should be lifted."

The league's letter says it has tried to interview the players on at least seven occasions, and each time the players' association has told them the players refuse to participate. The NFLPA submitted statements from the players — with the belief that would be enough to satisfy cooperation with the investigation — but the NFL swatted that down quickly as well. Again, per the letter:

"Rather than eliminate the need for interviews, the players' plainly deficient statements simply underscore the importance of obtaining their full cooperation."

The players have maintained that they are innocent, and when asked about this last month, Matthews sounded more inconvenienced by it all than anything else. This was his response when asked about the investigation, per the Milwaukee Journal-Sentinel, in late July: "

"I have no idea," Matthews said when asked what information he could provide. "We asked the same questions (to them). Maybe it's to conduct a formal investigation. I don't know. It's annoying, there's no doubt about that."

He added later in the piece: "If it was up to me this thing would be behind us a long time ago."

Uh, it sounds like it was up to him? Am I missing something? Maybe the NFLPA doesn't want him to talk?

In any event, this sounds reasonably serious — if you think a suspension of star players next week is serious, anyway. Maybe the NFL is just frustrated. But if Matthews, Peppers and the Packers think the NFL is just bluffing, they might want to remember this is a league that doled out a four-game suspension to one of its all-time greats for allegedly deflating footballs.

That's what can happen when the NFL doesn't like the way you cooperate.