The X-Factor: Minnesota Vikings defense

The Minnesota Vikings’ defense will be the X-Factor on Sunday.

They opened the season with an impressive showing in a victory over the St. Louis Rams (34-6), before the Vikings lost to New England (30-7) and New Orleans (20-9).

Against the Saints, the unit kept the Vikings in the game until referees made a questionable call on a sack of quarterback Drew Brees, who was taken to the ground by cornerback Captain Munnerlyn.

The group features a stout front seven that usually features linebacker Chad Greenway, who played last week with a broken rib and broken left hand against the Saints.

“He’s a tough kid,” Minnesota coach Mike Zimmer said. “Chad is a very smart guy. He’s a good competitor. He kind of helps keeps this team together.”

Greenway will not play against the Falcons, ending his streak of 90 consecutive starts, which was the longest active streak among NFL linebackers.

But the Vikings have a strong defensive line that consists of ends Brian Robison and Everson Griffen and tackles Linval Joseph and Sharrif Floyd. They also use linebacker Anthony Barr, the ninth pick in the 2014 draft, to rush the passer.

Barr could call the signals with Greenway out.

“We need to play better than we did against the Saints, but we have seven or eight new starters on this defense from a year ago,” Zimmer said. “We are still gelling. Floyd is a second-year guy who is kind of coming into his own a little bit. … Defensively, we are still kind of a work in progress.”

Minnesota’s defense ranks in the bottom half of the league in all key stats — total yards (335.3 per game), passing yards (225.3 per game), rushing yards (110 per game) and points (18.7 per game).