Agree with the poster that mentioned injury from heat stroke. My son suffered heat stroke in a cross country race - he completed the race, but collapsed at the finish line.
He had been been ill and running a fever that week, but felt obligated to run for the team. While the temperature had been in the 30-40's that week, the afternoon of the race the temperature soared into the 80's on an extremely hilly, treeless course.
The following week he attempted to run in championships and had a difficult time. That wasn't surprising, however, the problems had just begun. As the weeks went on, he couldn't lift his legs and keep his form after running more than a few minutes. Doctors discovered he had tiny muscle tears throughout his body caused by the dehydration from the heat stroke. As he would run, the mitochondria (the energy producing part of the cell) were literally leaking out, leaving his muscles very weak.
The solution - NO running, lifting weights, and so forth until the muscles had a chance to recover and heal. In my son's case, this meant no exercise whatsoever for at least 6 weeks. The good news is he was able to return to running and ended up having a great outdoor season.
I am not saying there isn't a mental aspect involved, because depression can certainly become an issue. However, my son's coach kept implying it was all a "mental" thing with him. That implication totally played with my son's head and it was quite a relief to discover it was mainly a very physical problem. Bekele's symptoms seem eerily familiar to the ones my son complained of. Perhaps he should seek out another doctor's opinion. I wish him the best.