I will offer some more advice on this soon but as a general comment: If this guys had no prior issue then there is not a justification that he should be considered 'weak' in an overall sense in this area. His pain might just because he is reintroducing some load on a damaged bit of tissue that is still healing, or even has healed but is still sending afferent information up to the brain due to it's non-use.

I agree that eccentric training, especially to soleus, initially both legs at the same time, later on single leg (to add in Tibialis Post. and Peroneal balance) would be useful in desensitizing the area. One must be able to prove weakness if prescribing strengthening. In this case it might not be weak and might just need a graded return to activity levels. Think of how sore things are the first day after skiing for the season, or after that first aerobics class... pretty sore.