Thomas apparently suffered the injury during a private workout with the New Orleans Saints last week, according to Aaron Wilson of the Baltimore Sun.
The exact effect of the knee injury on his draft stock is impossible to determine, but it has likely cost him millions of dollars. Given that the injury occurred in April, Thomas will certainly miss offseason workouts and possibly the entire 2014 season. Even with an Adrian Peterson-esque six-month recovery, Thomas will miss the season's first month, and most ACL recoveries take closer to a year. If that's the case, any team considering drafting him will have to assume that he won't be available until 2015.