The detail of the injury was first reported by the NFL Network and confirmed by ESPN. Rankins will have surgery, and is expected to miss 6-8 weeks; he will get a second opinion, sources told ESPN's Adam Schefter.
Rankins, who was drafted with the 12th overall pick, went down with the injury during a set of live goal-line drills.
The injury is another big blow to a Saints defense that also lost second-year pass-rusher Hau'oli Kikaha to a knee injury this summer. The Saints were woeful on defense last season, ranking last in the NFL in yards per rush and yards per pass play. Rankins was expected to be a big part of their turnaround.
The 6-foot-2, 305-pound Rankins is an athletic and versatile big man who had 14 sacks and 26.5 tackles for loss over his final two years at Louisville.
Rankins has mostly been working with the first-string defense this summer, though he has been rotating at the three-technique spot with another one of the Saints' key acquisitions -- veteran free agent Nick Fairley. Depending on the severity of Rankins' injury, Fairley could become much more important to the Saints' defense.
Rankins had been off to a solid start in camp so far, highlighted by his interception against Tom Brady in last week's joint practices with the New England Patriots. His athleticism has been evident -- though he has still been facing the normal rookie highs and lows.
Some good news Monday for the Saints: A source told ESPN Insider Adam Schefter that linebacker Stephone Anthony, who suffered a leg injury last week, could miss a couple of weeks but "absolutely is expected back by the start of the season."