Breakout rookie Marshon Lattimore (ankle) and second-year pro Ken Crawley (abdomen) have both been ruled out after not practicing all week. The Saints (8-2) also must make do without starting defensive end Alex Okafor, who was placed on injured reserve this week with a torn Achilles.
"We'll have contingency plans for whoever we have available to us. And we'll have a good plan to go out and execute against the Rams," Saints defensive coordinator Dennis Allen said. "I think one of the good things is we've developed some depth here, hopefully so that we can withstand some of the injury concerns.
"You never know when you're gonna be called on. That's part of that, as everybody says, that 'next man up' philosophy. And that's really the way that this league is."
The Saints have survived injuries the past two months. The cornerback position is thinner than most after they also lost former starter Delvin Breaux to injured reserve with a broken fibula during the preseason.
Young backups P.J. Williams and De'Vante Harris will likely start on Sunday, with veteran Sterling Moore also in the mix after re-signing with New Orleans on Monday. Vaccaro will likely serve as the nickel cornerback, as he has done for most of the year when healthy.
Last week, after Lattimore was injured in the first quarter (while breaking up a pass in the end zone, no less) the Saints went on to give up more than 300 yards and three touchdown passes to the Washington Redskins' Kirk Cousins in a dramatic 34-31 overtime victory.
Lattimore, just 21 years old, has been one of the top cornerbacks in the NFL this season -- and one of the main reasons why New Orleans has the second-best pass defense in the league since Week 3 (167 passing yards allowed per game in that span).
Lattimore, who was drafted with the 11th overall pick, is a front-runner for the NFL's Defensive Rookie of the Year award, with two interceptions (one returned for a touchdown), nine pass defenses and a forced fumble.
The Rams offense, meanwhile, has been just as surprising as the New Orleans defense, ranking fifth in the NFL this season with 375.4 yards per game and second in the league with 30.3 points per game.
Los Angles, however, will also be missing top receiver Robert Woods this week after he was ruled out with a shoulder injury.