Knee Injury

I went out to the park alone late this morning to run 8 miles on the trails. At about 3 to 4 miles into the run, I tripped on a root and caught myself on a small tree. Somehow, I hurt my left knee. I tried to continue running, but ended up walking most of the way back in. It is swollen around my left knee cap. When I got home, I put ice on it and treated it with some stuff. Hopefully, it will be okay by the marathon next Sunday. It is frustrating. I have been addicted to trail running for about 16 years, but trails have been the source of most of my injuries.