Re: Runners: Please help my friend!
I had posterior knee pain for the longest time, to the point of not being able to run, and I thought it was a pretty serious injury. Until a chiropractor told me I was just inflexible. A couple weeks of serious hamstring stretching, at least 3 times a day, later and it was gone.
But yeah, there's not much you can do, training wise, for a marathon 3 weeks away. So I wouldn't sweat it. And your friend may very well have an injury, so take this advice with a grain of salt. But it won't hurt to try stretching and rest first.