The Saints are expected to place cornerback Patrick Robinson on injured reserve with a broken ankle, sources tell Ian Rapoport and Mike Garafolo of NFL.com (on Twitter). The Saints initially thought Robinson was dealing with a sprain, but further tests uncovered more serious damage. 
It’s not immediately clear whether the injury will rule Robinson out for the year. Per league rules, Robinson can return after spending at least eight weeks on IR, so he could be back in the lineup later this year if he heals up quickly.
The injury will impact the Saints for however long Robinson is out of action. Through three weeks, the Saints have one of the worst-ranked pass defenses in the NFL, and the loss of their top slot man will hurt.
After winning a championship with the Eagles, Robinson inked a four-year deal with the Saints in March. Last year, he graded out as Pro Football Focus’ No. 6 ranked CB.