I'm a type 1 diabetic. It shouldn't alter his lifestyle too much as a professional footballer. It will take him a bit to get used to the condition, but with the medical staff he should be fine. Before a game he'll need to drink something high in sugar and possibly at half time. I think asthma would be more of a concern (for an athlete). Gary Mabbutt was a diabetic, and I think Steve Redgrave too. The medical team will have him under watch and it shouldn't affect his performances if he diets correctly. The worry would be to not have enough sugar cos to be hypoglycemic (levels too low) is akin to being extremely drunk - staggering, incoherent, unaware of the situation around you, whereas hyperglycemic (sugar levels too high) feels more like aching muscles and you can run that off, or adapt your warmup slightly. I might have oversimplified this but it should not affect his ability to play football to his highest level.