Since the season opened, the Buffalo Bills' Mario Williams has been complaining about a nagging wrist injury. But the fact that the Bills have not listed Williams on any of their injury reports, including last week's, has caught the attention of executives around the league and the NFL itself.

The NFL is investigating why Williams, who landed $50 million in guaranteed money this offseason, has publicly complained about his wrist as recently as last week, yet he still is not on Buffalo's injury report.

NFL spokesman Greg Aiello said Sunday that "the club says he is not injured. We will follow up this week to obtain a formal explanation."

The Bills said Williams has not missed any practice reps and there never was a doubt he would play in each game.

Yet the NFL's injury report policy says "significant or noteworthy injuries must be listed" regardless.

"Even if the player takes all the reps in practice, and even if the team is certain that he will play in the upcoming game," the rule states. "This is especially true of key players and those players whose injuries have been covered extensively by the media. ... This policy is of paramount importance in maintaining the integrity of the NFL."

Information from The Associated Press was used in this report.