Tannehill told reporters Wednesday he felt his knee shift, and immediately knew the injury could lead to lost playing time.
"I knew it wasn't good," Tannehill said. "Honestly, I wasn't really processing all of that. I just knew it was bad and I don't know, kind of went to a shock a little bit of, 'I can't believe this is happening.'"
Tannehill suffered a torn ACL, which led to the Dolphins placing him on season-ending injured reserve.
With a full regular season and offseason to rehabilitate his knee, however, Tannehill prefers to look forward and not relive the moment he went down.
'It's been a long time since then and it's tough to go back to that state," he said, "but I'm a long way from there and feeling really good right now."
The Dolphins quarterback also recently visited with the medical team that performed his knee surgery in Dallas and received a full clean bill of health.
"I went back last week and got fully cleared to play football," Tannehill said. "I'm cleared to play football, so whatever that entails I can go do it."
Meanwhile, the Dolphins on Tuesday tweeted a short video clip of Tannehill taking the practice field for organized team activities, and he wasn't wearing a protective sleeve or brace on his knee.
But the quarterback said Wednesday that he will take preventive measures to protect his surgically repaired knee from hits to the side by wearing a protective brace during the regular season.
"The brace can help prevent that, minimize that damage and hopefully make it a non-issue moving forward," Tannehill said.