Tannehill originally suffered a partially torn ACL during last season's Week 14 game against the Cardinals, and he was wearing a brace on his knee during training camp -- right up till eight days ago when he landed awkwardly during a non-contact drill that left him limping.
But after the original injury, the Dolphins chose to rest Tannehill's knee instead of opting for late-season surgery. That turned out to be the wrong decision. You could argue that had Tannehill undergone the surgery, he could still be recovering, but Joe Flacco and Carson Palmer -- both older than Tannehill -- rebounded from similar surgical procedures to play at a high level the next season.
A source even went so far as to tell ESPN's Adam Schefter that Tannehill's knee was an accident waiting to happen.
"One source said Thursday that, because Tannehill did not repair his partially torn ACL during the offseason, his knee was 'a ticking time bomb' that was going to go off at any time," Schefter reported last week.
Now the Dolphins are on to Plan B, which involves reuniting coach Adam Gase with Jay Cutler after the team lured him out of retirement. And while the two worked well together in Chicago two years ago, there's no guarantee that they can recapture that magic in time to help the Dolphins threatened for a wild-card berth in back-to-back seasons.