According to Jakes father, Scott Locker, who was on KJR today, the MRI revealed a slight tear/strain to the hamstring. Supposedly it happened in a good place and they are pretty sure he will be back to practice some time next week, in other words he should be fine for the Oregon game.
This sounds like a grade one hamstring pull, and the prognosis for most of us would be one to three weeks. For a young athlete like Jake who heals quickly, and has the best medical care available you should expect to see him back out there by Wednesday, or Thursday.
So the news is about as good as you can hope for. Jake won't miss a lot of practice time, and he should be ready for Oregon.