What Causes Pain In Foot And Calf Muscles?

My son who is 15 years old was an academy soccer player at a professional premier league club in the UK - he was considered of sufficient ability to be told he would be offered a scholarship. In June of last year he began getting pain in the arch of both feet and on the outside of his calf muscles in both legs specifically when he plays football on grass or on 3g astro turf. The pain comes on every time he plays after approximately 15 minutes and is so bad he cannot continue. This eventually forced him to leave the academy. On a day to day basis he is pain free and has only once experienced slight pain when walking. Inexplicably he has been able to play and train soccer on a sprung wooden gym floor for up to two hours with no pain or adverse adverse affects. To explain briefly, during the past eleven months he has had. 1. Extensive physiotherapy. 2. He has seen two podiatrists and a podiatric surgeon who prescribed standard and custom made orthotics none were effective 3. He has seen a specialist in compartment syndrome who ruled that out as the cause.( but did not do pressure test) 4. He has had MRI scan of feet and legs – no problems were found. 5. He has had both XRAY and CT scans of the feet – no problems were found. 6. He was tested for tarsal tunnel syndrome – the test was negative. 7. He has had an MRI on his lumbar spine again negative. We are at a loss as to what the problem could be