Has the liver problem been caused by the training?
Has his decline in performance been caused by the liver problem?
If the liver problem isn’t training related (is there something I’m missing out on because you seem to make the assumption it’s a result of his training?) then there’s a very real possibility that it’s not “overtraining” that’s causing the slump in performance, but a very real medical condition.
Of course the training may have made the inital problem worse, but to imply that it caused it in the first place is a little bit of a stretch in my (un-medically educated) opinion.