Tannehill injured his knee in training camp on Aug. 3, per Barry Jackson of the Miami Herald. The 29-year-old fell to the ground on a non-contact play when his left knee appeared to buckle.
NFL Network's Aditi Kinkhabwala initially provided some optimism for Tannehill and the Dolphins when she reported there was no structural damage to the knee.
However, ESPN's Adam Schefter reported the Dolphins' "fear" was Tannehill would require season-ending surgery.
One source told Schefter that Tannehill's knee was "a ticking time bomb that was going to go off at any time" after he opted not to have it surgically repaired following a partial ACL tear during a Week 14 game against the Arizona Cardinals last season. The injury caused him to miss the final four contests, including the AFC Wild Card Game against the Pittsburgh Steelers.
According to Schefter, if Tannehill decided against surgery, he would have had to rest for six to eight weeks before attempting to play on his knee once again.
Losing Tannehill for the entire campaign is a major blow as the Dolphins look to make a second consecutive postseason appearance. Prior his partial ACL tear, he was having a strong 2016 season with a career-high 67.1 completion percentage and 7.7 passing yards per attempt.
Tannehill does have his flaws—including throwing at least 12 interceptions in each of his first five NFL seasons—but he's had more positives than negatives throughout his career to this point.
Per Pro Football Focus' Ryan Smith, Tannehill finished third out of 37 qualified quarterbacks in overall grade when he released the ball in 2.5 seconds or less.
Now that the Dolphins know Tannehill's fate, Jay Cutler will be running the offense.
This isn't the scenario Miami's coaching staff and front office wanted to find the team in right out of the gate in 2017. But Cutler has experience under head coach Adam Gase and talent around him, so Tannehill's premature exit doesn't have to destroy the Dolphins' playoff hopes.