Vinnie Sunseri has two pick-sixes for the Alabama defense this season. (USATSI)

Alabama has lost a major part of its defense for the rest of the season.

Safety Vinnie Sunseri will miss the rest of the 2013 season after suffering a torn knee ligament. Alabama coach Nick Saban confirmed the injury during his Monday news conference, saying Sunseri would undergo surgery on his left knee.

Sunseri, a junior, left Saturday's game during the first quarter after suffering the injury on special teams.

Sunseri's loss is a big blow to an Alabama defense that has reestablished its dominance over the last month. In its five games since allowing 628 yards and 42 points against Texas A&M, the Alabama defense has allowed a total of 1,085 yards (217 per game) and 16 points.

Sunseri, who was just named to CBSSports.com's Midseason All-American team, was a big part of that. On the season Sunseri has 20 tackles, four passes broken up and two interceptions. Sunseri has returned both of his interceptions for touchdowns.

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Landon Collins, a sophomore, will replace Sunseri in Alabama's starting lineup. Collins was a five-star prospect in Alabama's 2012 recruiting class, and was considered one of the top ten high school players in his class.