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Arkansas tight end Jack Kraus (87) works to keep LSU linebacker Arden Key (49) at bay in the second half of LSU's 33-10 win over Arkansas, Saturday, November 11, 2017, at LSU's Tiger Stadium in Baton Rouge, La.

Arden Key is officially going pro.

LSU’s All-American edge rusher and projected top 20 NFL pick announced the expected news Thursday on social media, officially ending a three-year college career that included many highs and lows.

Key, a Georgia native, set the single-season LSU sack record (12) in 2016 as a sophomore before a drama-filled junior year produced four sacks and five missed games. Key did not participate in the Citrus Bowl against Notre Dame on Monday; coach Ed Orgeron said last month said it was because of his star’s health.

Key missed the final two games of the regular season with a knee injury, and he underwent surgery on a broken pinky finger immediately after the regular season.

"Our sincere gratitude goes out to all of the LSU fans, the state of Louisiana, Coach O and staff, administration and most of all my brothers," Key said in the post. "A special thank you to Coach Miles for giving me the opportunity to become a Tiger. ... Excited to start my new journey and prayers that my LSU fam will continue to support me. To LSU Football, bring our state of Louisiana a national championship."

There are plenty of possibilities to replace Key, but he leaves a gaping hole. Redshirt freshman Ray Thornton and true freshman K’Lavon Chaisson rotated in replacing him late this season. Andre Anthony, an Edna Karr product, also played the Buck outside linebacker spot before sustaining a season-ending injury during camp.

The Tigers signed a handful of players who could help fill Key’s void, including Jarell Cherry and junior-college transfer Travez Moore.

A dynamic and speedy player, Key finished his LSU career tied for third all-time at the school in sacks with 21. His junior season was somewhat peculiar and shrouded in secrecy. He took a leave of absence in the spring for what the school called “personal reasons,” had shoulder surgery in late May and missed all of summer workouts.

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He missed the first two games of the season while continuing to recover from the surgery and then broke his pinky finger in a game in early October, playing with the injury for the next two months before the knee injury cropped up against Arkansas.

Key has not been made available to reporters since December 2016.

Despite off-the-field and injury questions, the 6-6, 250-pound Key is still projected as a first-round selection in the 2018 NFL draft at AT&T Stadium in Arlington, Texas. He’s ranked by many draft analysts as the top edge rusher in the draft, with the potential for selection in the top 10.

The worry with Key is not on the field, NFL draft analysts say. Key’s leave of absence in the spring is coupled with at least one game in which he was suspended. His athleticism and potential as an NFL pass rusher is somewhat hurt by the off-the-field questions. They make his exact draft projection somewhat murky.

“On the hoof, he’s beautiful,” said Matt Miller, an NFL draft analyst for Bleacher Report. “Built like Jason Taylor, exactly what you want a defensive end to look like. Long, twitchy. Then you have the leaving school, shoulder injury and now the (knee) injury. Hurt players tend to stay hurt. Guys who have 2-3 injuries in school … it’s hard to overcome that.

“He is incredibly talented. Fits exactly what you want form a defensive end. It’s a matter (of), Is he ever going to put it together?”

A handful of other LSU players are expected to leave, Orgeron said. The list includes running back Derrius Guice and cornerbacks Donte Jackson and Kevin Toliver. Offensive linemen Toby Weathersby, Will Clapp and Garrett Brumfield also all filed requests for an evaluation grade with the NFL Draft College Advisory Committee. 

Follow Ross Dellenger on Twitter, @RossDellenger.