Hard to say IT band or other issue.... either would be chronic over use injury. Adding to pp, make sure you stretch after each and every run. Twice a day roll the calf, ham, quads and IT areas.
Today and for the next day or two, RICE, Rest, Ice, Compression and elevation
Try to take it easy on the knee. Ice the knee 2-4 times a day for 30 minutes. If you have an Ace bandage, wrap the knee and kick back and enjoy some tv this afternoon. Consider taking an into-inflammatory for a day or two to help with the inflammation.
It's hard to say, but this has probably been a long season coming. If you did not notice anything happen on the run, it is more than likely an over use injury. Taper will help heal up the knee and by race day this may be a distant memory.
Good Luck