They said something pretty funny about this on ESPN today. They said that TO was just trying to draw attention to himself by pretending to be hurt, so that he would open his Dallas career at home against the 49ers. I think he might have a little bit of tightness in his hamstring but anyone else could play with the same injury.
The Dallas organization said he won't miss any games during the pre season, and the rumour of him having a hamstring strain is false, and he should be ready to go by the first game of the pre season, also he probably won't play a lot anyways. Because it is the pre season.