He has chose to have surgery to fix a torn ACL in his left knee, reports the Miami Herald's Armando Salguero.
The Dolphins and Tannehill were hoping his knee, with the aid of a brace, would be stable enough to last the season.
As it's been speculated since last week, Ryan Tannehill will undergo surgery to fix the damage to his twice-injured ACL on his left knee. Tannehill sustained the injury on August 3 on a non-contact play when he planted his left leg awkwardly while rolling to his right.
The 29-year-old initially injured his knee against the Arizona Cardinals in December, partially tearing the ACL. Last season, the quarterback suffered a partial ACL tear on that same knee but he opted for stem cell treatment instead of undergoing surgery.
The Dolphins lured quarterback Jay Cutler out of retirement and signed him to a reported one-year, $10 million deal Monday.
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Last season, Cutler played in just five games because of thumb and shoulder injuries.
This is the first major surgery for Tannehill's, and it comes at a time when it seemed he was poised to have the best season of his career.
Coach Adam Gase believes Tannehill can and will help new quarterback Jay Cutler adjust to his projected role as starter. Cutler, 34, might make his Dolphins debut in their second exhibition game next Thursday.
The Dolphins signed Tannehill to a six-year, $96 million extension in May 2015 that signed him through the 2015 season.