Miles wouldn't disclose the nature of Mettenberger's injury, but ESPN reported he suffered a torn anterior cruciate ligament in his left knee, as well a sprained medial collateral ligament in the same knee.
The injury happened during the Tigers' 31-27 victory last week over Arkansas when he was pinned under a defender.
"We are very disappointed for Zach," Miles said. "He's been a tremendous leader for our team and he's as competitive a guy as I have ever been around. He's had a great impact on our program."
In his final season with LSU, Mettenberger compiled 3,082 passing yards with 22 touchdowns and eight interceptions.
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