Broken ankle sends Saints CB Patrick Robinson to IR

METAIRIE, La. -- The New Orleans Saints' struggling pass defense took another hit on Tuesday with news that veteran nickel cornerback Patrick Robinson will be placed on injured reserve with a broken left ankle.

A source confirmed the news, which was first reported by the NFL Network. Robinson is expected to be out for the season.

Robinson, who was one of the Saints' top free-agent signings this offseason, was carted off the field during Sunday's 43-37 overtime victory versus the Atlanta Falcons.

He is scheduled to undergo surgery on Wednesday.

The Saints are 2-1, but their pass defense has struggled mightily this season. They have allowed an opponents' passer rating of 141.7, 20 points higher than any other defense in the NFL.

They also are yielding 336.7 passing yards per game, which ranks 30th in the NFL. And they have allowed 10 touchdown passes, which is tied for the most in the league.

It's unclear how much Robinson played a role in those struggles -- since he was brought back to New Orleans to play in the slot. Most of the Saints' troubles have come on deep passes against their outside cornerbacks.

Regardless, losing a reliable veteran from the mix will hurt a New Orleans team that has already been laboring at the position. Last week, the Saints replaced starting cornerback Ken Crawley with veteran backup P.J. Williams on the outside -- only to switch back after Williams allowed two first-half touchdown passes to Falcons rookie wideout Calvin Ridley.

Robinson, 31, who began his career as a first-round draft pick with the Saints from 2010 to 2014, has developed into one of the best slot cornerbacks in the NFL, which is specifically why the Saints brought him back on a four-year, $20 million contract.

The 5-foot-11, 191-pounder had arguably the best season of his career last year for the Philadelphia Eagles, helping them win a Super Bowl.

The Saints will be tested immediately without him on Sunday in New York against a Giants offense that features both a dynamic playmaker in Odell Beckham Jr. and a threatening No. 2 receiver in Sterling Shepard, who does some of his best work in the slot.

It's unclear who will replace Robinson in the slot. The Saints held some auditions on Tuesday. They could consider Williams. Or they could consider relying heavily on three-safety packages, which they have done often in the past.

The Saints were deep with cornerback options this summer. But they released veteran Marcus Williams and rookie fifth-round draft pick Natrell Jamerson, among others who got picked up by other teams. Then they just released second-year cornerback Arthur Maulet heading into the weekend and lost him on waivers to the Indianapolis Colts.