In his prelim loss to Manny Gamburyan at UFC 79 Nate Mohr was in a leg lock when he let out a scream and the fight was stopped.  My initial reaction was that Manny must have switched from an ankle lock to a heel hook and damaged Nate's knee.  During the PPV broadcast no camera angle was shown that really revealed how Manny had the hold locked on.

However MMAWeekly reports that it was more of a freak accident while attempting to improve his position:

Once again a Gamburyan fight ends on an injury.  It's unfortunate, but a part of the game.

The question for Mohr (now 1-2 in the octogon) is if the UFC will see past the injury and give him another shot.  If they do Nate will have to shore up his submission game as all 5 of his losses have come via chokes and leg locks.