Word during the game was that he had an MCL sprain and that the trainers were fitting him for a brace for a possible return. The team of course did the smart thing and held him out.
I suppose that is the joy of scheduling a weak opponent at this point in the season. In a worst case scenario like this when your superstar gets hurt you can afford to sit him for a game rather than risk further injury.
Hopefully the injury really wasn't too serious and Miller will be back in action next week against Cal (although they really won't need him till they face off against Wisconsin on the 28th).