"From the first time I saw the Missy injury video I thought it was leg more than head. I interned in sports medicine in college, and it looked to me like the ankle brought her down and she may have hit her head as she came down."...but those scenes are from the Reward Challenge and if you watch in slow motion you can see that Missy does NOT hit her head and her Left ankle (the one with the sleeve on in the Oct photo) looks fine too. I suspect Missy might get dragged through the challenge like Chet in Micronesia and that might change her opinion about Jon but I'm doubt she gets injured badly in the Reward Challenge though maybe she initially injures her left ankle in the RC.
The Press Release identifies an ankle injury:
"Also, a sudden ankle injury could lead to a medevac just days before the game ends,"
...and we know Jeff tends to Missy's left ankle and the doctor arrives at the Immunity Challenge